// SPDX-License-Identifier: GPL-2.0-only #include <linux/init.h> #include <linux/mm.h> #include <linux/spinlock.h> #include <linux/smp.h> #include <linux/interrupt.h> #include <linux/export.h> #include <linux/cpu.h> #include <linux/debugfs.h> #include <linux/sched/smt.h> #include <linux/task_work.h> #include <linux/mmu_notifier.h> #include <linux/mmu_context.h> #include <linux/kvm_types.h> #include <asm/tlbflush.h> #include <asm/mmu_context.h> #include <asm/nospec-branch.h> #include <asm/cache.h> #include <asm/cacheflush.h> #include <asm/apic.h> #include <asm/msr.h> #include <asm/perf_event.h> #include <asm/tlb.h> #include "mm_internal.h" #ifdef CONFIG_PARAVIRT # define STATIC_NOPV #else # define STATIC_NOPV static # define __flush_tlb_local native_flush_tlb_local # define __flush_tlb_global native_flush_tlb_global # define __flush_tlb_one_user(addr) native_flush_tlb_one_user(addr) # define __flush_tlb_multi(msk, info) native_flush_tlb_multi(msk, info) #endif /* * TLB flushing, formerly SMP-only * c/o Linus Torvalds. * * These mean you can really definitely utterly forget about * writing to user space from interrupts. (Its not allowed anyway). * * Optimizations Manfred Spraul <manfred@colorfullife.com> * * More scalable flush, from Andi Kleen * * Implement flush IPI by CALL_FUNCTION_VECTOR, Alex Shi */ /* * Bits to mangle the TIF_SPEC_* state into the mm pointer which is * stored in cpu_tlb_state.last_user_mm_spec. */ #define LAST_USER_MM_IBPB 0x1UL #define LAST_USER_MM_L1D_FLUSH 0x2UL #define LAST_USER_MM_SPEC_MASK (LAST_USER_MM_IBPB | LAST_USER_MM_L1D_FLUSH) /* Bits to set when tlbstate and flush is (re)initialized */ #define LAST_USER_MM_INIT LAST_USER_MM_IBPB /* * The x86 feature is called PCID (Process Context IDentifier). It is similar * to what is traditionally called ASID on the RISC processors. * * We don't use the traditional ASID implementation, where each process/mm gets * its own ASID and flush/restart when we run out of ASID space. * * Instead we have a small per-cpu array of ASIDs and cache the last few mm's * that came by on this CPU, allowing cheaper switch_mm between processes on * this CPU. * * We end up with different spaces for different things. To avoid confusion we * use different names for each of them: * * ASID - [0, TLB_NR_DYN_ASIDS-1] * the canonical identifier for an mm, dynamically allocated on each CPU * [TLB_NR_DYN_ASIDS, MAX_ASID_AVAILABLE-1] * the canonical, global identifier for an mm, identical across all CPUs * * kPCID - [1, MAX_ASID_AVAILABLE] * the value we write into the PCID part of CR3; corresponds to the * ASID+1, because PCID 0 is special. * * uPCID - [2048 + 1, 2048 + MAX_ASID_AVAILABLE] * for KPTI each mm has two address spaces and thus needs two * PCID values, but we can still do with a single ASID denomination * for each mm. Corresponds to kPCID + 2048. * */ /* * When enabled, MITIGATION_PAGE_TABLE_ISOLATION consumes a single bit for * user/kernel switches */ #ifdef CONFIG_MITIGATION_PAGE_TABLE_ISOLATION # define PTI_CONSUMED_PCID_BITS 1 #else # define PTI_CONSUMED_PCID_BITS 0 #endif #define CR3_AVAIL_PCID_BITS (X86_CR3_PCID_BITS - PTI_CONSUMED_PCID_BITS) /* * ASIDs are zero-based: 0->MAX_AVAIL_ASID are valid. -1 below to account * for them being zero-based. Another -1 is because PCID 0 is reserved for * use by non-PCID-aware users. */ #define MAX_ASID_AVAILABLE ((1 << CR3_AVAIL_PCID_BITS) - 2) /* * Given @asid, compute kPCID */ static inline u16 kern_pcid(u16 asid) { VM_WARN_ON_ONCE(asid > MAX_ASID_AVAILABLE); #ifdef CONFIG_MITIGATION_PAGE_TABLE_ISOLATION /* * Make sure that the dynamic ASID space does not conflict with the * bit we are using to switch between user and kernel ASIDs. */ BUILD_BUG_ON(TLB_NR_DYN_ASIDS >= (1 << X86_CR3_PTI_PCID_USER_BIT)); /* * The ASID being passed in here should have respected the * MAX_ASID_AVAILABLE and thus never have the switch bit set. */ VM_WARN_ON_ONCE(asid & (1 << X86_CR3_PTI_PCID_USER_BIT)); #endif /* * The dynamically-assigned ASIDs that get passed in are small * (<TLB_NR_DYN_ASIDS). They never have the high switch bit set, * so do not bother to clear it. * * If PCID is on, ASID-aware code paths put the ASID+1 into the * PCID bits. This serves two purposes. It prevents a nasty * situation in which PCID-unaware code saves CR3, loads some other * value (with PCID == 0), and then restores CR3, thus corrupting * the TLB for ASID 0 if the saved ASID was nonzero. It also means * that any bugs involving loading a PCID-enabled CR3 with * CR4.PCIDE off will trigger deterministically. */ return asid + 1; } /* * Given @asid, compute uPCID */ static inline u16 user_pcid(u16 asid) { u16 ret = kern_pcid(asid); #ifdef CONFIG_MITIGATION_PAGE_TABLE_ISOLATION ret |= 1 << X86_CR3_PTI_PCID_USER_BIT; #endif return ret; } static inline unsigned long build_cr3(pgd_t *pgd, u16 asid, unsigned long lam) { unsigned long cr3 = __sme_pa(pgd) | lam; if (static_cpu_has(X86_FEATURE_PCID)) { cr3 |= kern_pcid(asid); } else { VM_WARN_ON_ONCE(asid != 0); } return cr3; } static inline unsigned long build_cr3_noflush(pgd_t *pgd, u16 asid, unsigned long lam) { /* * Use boot_cpu_has() instead of this_cpu_has() as this function * might be called during early boot. This should work even after * boot because all CPU's the have same capabilities: */ VM_WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_PCID)); return build_cr3(pgd, asid, lam) | CR3_NOFLUSH; } /* * We get here when we do something requiring a TLB invalidation * but could not go invalidate all of the contexts. We do the * necessary invalidation by clearing out the 'ctx_id' which * forces a TLB flush when the context is loaded. */ static void clear_asid_other(void) { u16 asid; /* * This is only expected to be set if we have disabled * kernel _PAGE_GLOBAL pages. */ if (!static_cpu_has(X86_FEATURE_PTI)) { WARN_ON_ONCE(1); return; } for (asid = 0; asid < TLB_NR_DYN_ASIDS; asid++) { /* Do not need to flush the current asid */ if (asid == this_cpu_read(cpu_tlbstate.loaded_mm_asid)) continue; /* * Make sure the next time we go to switch to * this asid, we do a flush: */ this_cpu_write(cpu_tlbstate.ctxs[asid].ctx_id, 0); } this_cpu_write(cpu_tlbstate.invalidate_other, false); } atomic64_t last_mm_ctx_id = ATOMIC64_INIT(1); struct new_asid { unsigned int asid : 16; unsigned int need_flush : 1; }; static struct new_asid choose_new_asid(struct mm_struct *next, u64 next_tlb_gen) { struct new_asid ns; u16 asid; if (!static_cpu_has(X86_FEATURE_PCID)) { ns.asid = 0; ns.need_flush = 1; return ns; } /* * TLB consistency for global ASIDs is maintained with hardware assisted * remote TLB flushing. Global ASIDs are always up to date. */ if (cpu_feature_enabled(X86_FEATURE_INVLPGB)) { u16 global_asid = mm_global_asid(next); if (global_asid) { ns.asid = global_asid; ns.need_flush = 0; return ns; } } if (this_cpu_read(cpu_tlbstate.invalidate_other)) clear_asid_other(); for (asid = 0; asid < TLB_NR_DYN_ASIDS; asid++) { if (this_cpu_read(cpu_tlbstate.ctxs[asid].ctx_id) != next->context.ctx_id) continue; ns.asid = asid; ns.need_flush = (this_cpu_read(cpu_tlbstate.ctxs[asid].tlb_gen) < next_tlb_gen); return ns; } /* * We don't currently own an ASID slot on this CPU. * Allocate a slot. */ ns.asid = this_cpu_add_return(cpu_tlbstate.next_asid, 1) - 1; if (ns.asid >= TLB_NR_DYN_ASIDS) { ns.asid = 0; this_cpu_write(cpu_tlbstate.next_asid, 1); } ns.need_flush = true; return ns; } /* * Global ASIDs are allocated for multi-threaded processes that are * active on multiple CPUs simultaneously, giving each of those * processes the same PCID on every CPU, for use with hardware-assisted * TLB shootdown on remote CPUs, like AMD INVLPGB or Intel RAR. * * These global ASIDs are held for the lifetime of the process. */ static DEFINE_RAW_SPINLOCK(global_asid_lock); static u16 last_global_asid = MAX_ASID_AVAILABLE; static DECLARE_BITMAP(global_asid_used, MAX_ASID_AVAILABLE); static DECLARE_BITMAP(global_asid_freed, MAX_ASID_AVAILABLE); static int global_asid_available = MAX_ASID_AVAILABLE - TLB_NR_DYN_ASIDS - 1; /* * When the search for a free ASID in the global ASID space reaches * MAX_ASID_AVAILABLE, a global TLB flush guarantees that previously * freed global ASIDs are safe to re-use. * * This way the global flush only needs to happen at ASID rollover * time, and not at ASID allocation time. */ static void reset_global_asid_space(void) { lockdep_assert_held(&global_asid_lock); invlpgb_flush_all_nonglobals(); /* * The TLB flush above makes it safe to re-use the previously * freed global ASIDs. */ bitmap_andnot(global_asid_used, global_asid_used, global_asid_freed, MAX_ASID_AVAILABLE); bitmap_clear(global_asid_freed, 0, MAX_ASID_AVAILABLE); /* Restart the search from the start of global ASID space. */ last_global_asid = TLB_NR_DYN_ASIDS; } static u16 allocate_global_asid(void) { u16 asid; lockdep_assert_held(&global_asid_lock); /* The previous allocation hit the edge of available address space */ if (last_global_asid >= MAX_ASID_AVAILABLE - 1) reset_global_asid_space(); asid = find_next_zero_bit(global_asid_used, MAX_ASID_AVAILABLE, last_global_asid); if (asid >= MAX_ASID_AVAILABLE && !global_asid_available) { /* This should never happen. */ VM_WARN_ONCE(1, "Unable to allocate global ASID despite %d available\n", global_asid_available); return 0; } /* Claim this global ASID. */ __set_bit(asid, global_asid_used); last_global_asid = asid; global_asid_available--; return asid; } /* * Check whether a process is currently active on more than @threshold CPUs. * This is a cheap estimation on whether or not it may make sense to assign * a global ASID to this process, and use broadcast TLB invalidation. */ static bool mm_active_cpus_exceeds(struct mm_struct *mm, int threshold) { int count = 0; int cpu; /* This quick check should eliminate most single threaded programs. */ if (cpumask_weight(mm_cpumask(mm)) <= threshold) return false; /* Slower check to make sure. */ for_each_cpu(cpu, mm_cpumask(mm)) { /* Skip the CPUs that aren't really running this process. */ if (per_cpu(cpu_tlbstate.loaded_mm, cpu) != mm) continue; if (per_cpu(cpu_tlbstate_shared.is_lazy, cpu)) continue; if (++count > threshold) return true; } return false; } /* * Assign a global ASID to the current process, protecting against * races between multiple threads in the process. */ static void use_global_asid(struct mm_struct *mm) { u16 asid; guard(raw_spinlock_irqsave)(&global_asid_lock); /* This process is already using broadcast TLB invalidation. */ if (mm_global_asid(mm)) return; /* * The last global ASID was consumed while waiting for the lock. * * If this fires, a more aggressive ASID reuse scheme might be * needed. */ if (!global_asid_available) { VM_WARN_ONCE(1, "Ran out of global ASIDs\n"); return; } asid = allocate_global_asid(); if (!asid) return; mm_assign_global_asid(mm, asid); } #ifdef CONFIG_BROADCAST_TLB_FLUSH void mm_free_global_asid(struct mm_struct *mm) { if (!cpu_feature_enabled(X86_FEATURE_INVLPGB)) return; if (!mm_global_asid(mm)) return; guard(raw_spinlock_irqsave)(&global_asid_lock); /* The global ASID can be re-used only after flush at wrap-around. */ __set_bit(mm->context.global_asid, global_asid_freed); mm->context.global_asid = 0; global_asid_available++; } #endif /* * Is the mm transitioning from a CPU-local ASID to a global ASID? */ static bool mm_needs_global_asid(struct mm_struct *mm, u16 asid) { u16 global_asid = mm_global_asid(mm); if (!cpu_feature_enabled(X86_FEATURE_INVLPGB)) return false; /* Process is transitioning to a global ASID */ if (global_asid && asid != global_asid) return true; return false; } /* * x86 has 4k ASIDs (2k when compiled with KPTI), but the largest x86 * systems have over 8k CPUs. Because of this potential ASID shortage, * global ASIDs are handed out to processes that have frequent TLB * flushes and are active on 4 or more CPUs simultaneously. */ static void consider_global_asid(struct mm_struct *mm) { if (!cpu_feature_enabled(X86_FEATURE_INVLPGB)) return; /* Check every once in a while. */ if ((current->pid & 0x1f) != (jiffies & 0x1f)) return; /* * Assign a global ASID if the process is active on * 4 or more CPUs simultaneously. */ if (mm_active_cpus_exceeds(mm, 3)) use_global_asid(mm); } static void finish_asid_transition(struct flush_tlb_info *info) { struct mm_struct *mm = info->mm; int bc_asid = mm_global_asid(mm); int cpu; if (!mm_in_asid_transition(mm)) return; for_each_cpu(cpu, mm_cpumask(mm)) { /* * The remote CPU is context switching. Wait for that to * finish, to catch the unlikely case of it switching to * the target mm with an out of date ASID. */ while (READ_ONCE(per_cpu(cpu_tlbstate.loaded_mm, cpu)) == LOADED_MM_SWITCHING) cpu_relax(); if (READ_ONCE(per_cpu(cpu_tlbstate.loaded_mm, cpu)) != mm) continue; /* * If at least one CPU is not using the global ASID yet, * send a TLB flush IPI. The IPI should cause stragglers * to transition soon. * * This can race with the CPU switching to another task; * that results in a (harmless) extra IPI. */ if (READ_ONCE(per_cpu(cpu_tlbstate.loaded_mm_asid, cpu)) != bc_asid) { flush_tlb_multi(mm_cpumask(info->mm), info); return; } } /* All the CPUs running this process are using the global ASID. */ mm_clear_asid_transition(mm); } static void broadcast_tlb_flush(struct flush_tlb_info *info) { bool pmd = info->stride_shift == PMD_SHIFT; unsigned long asid = mm_global_asid(info->mm); unsigned long addr = info->start; /* * TLB flushes with INVLPGB are kicked off asynchronously. * The inc_mm_tlb_gen() guarantees page table updates are done * before these TLB flushes happen. */ if (info->end == TLB_FLUSH_ALL) { invlpgb_flush_single_pcid_nosync(kern_pcid(asid)); /* Do any CPUs supporting INVLPGB need PTI? */ if (cpu_feature_enabled(X86_FEATURE_PTI)) invlpgb_flush_single_pcid_nosync(user_pcid(asid)); } else do { unsigned long nr = 1; if (info->stride_shift <= PMD_SHIFT) { nr = (info->end - addr) >> info->stride_shift; nr = clamp_val(nr, 1, invlpgb_count_max); } invlpgb_flush_user_nr_nosync(kern_pcid(asid), addr, nr, pmd); if (cpu_feature_enabled(X86_FEATURE_PTI)) invlpgb_flush_user_nr_nosync(user_pcid(asid), addr, nr, pmd); addr += nr << info->stride_shift; } while (addr < info->end); finish_asid_transition(info); /* Wait for the INVLPGBs kicked off above to finish. */ __tlbsync(); } /* * Given an ASID, flush the corresponding user ASID. We can delay this * until the next time we switch to it. * * See SWITCH_TO_USER_CR3. */ static inline void invalidate_user_asid(u16 asid) { /* There is no user ASID if address space separation is off */ if (!IS_ENABLED(CONFIG_MITIGATION_PAGE_TABLE_ISOLATION)) return; /* * We only have a single ASID if PCID is off and the CR3 * write will have flushed it. */ if (!cpu_feature_enabled(X86_FEATURE_PCID)) return; if (!static_cpu_has(X86_FEATURE_PTI)) return; __set_bit(kern_pcid(asid), (unsigned long *)this_cpu_ptr(&cpu_tlbstate.user_pcid_flush_mask)); } static void load_new_mm_cr3(pgd_t *pgdir, u16 new_asid, unsigned long lam, bool need_flush) { unsigned long new_mm_cr3; if (need_flush) { invalidate_user_asid(new_asid); new_mm_cr3 = build_cr3(pgdir, new_asid, lam); } else { new_mm_cr3 = build_cr3_noflush(pgdir, new_asid, lam); } /* * Caution: many callers of this function expect * that load_cr3() is serializing and orders TLB * fills with respect to the mm_cpumask writes. */ write_cr3(new_mm_cr3); } void leave_mm(void) { struct mm_struct *loaded_mm = this_cpu_read(cpu_tlbstate.loaded_mm); /* * It's plausible that we're in lazy TLB mode while our mm is init_mm. * If so, our callers still expect us to flush the TLB, but there * aren't any user TLB entries in init_mm to worry about. * * This needs to happen before any other sanity checks due to * intel_idle's shenanigans. */ if (loaded_mm == &init_mm) return; /* Warn if we're not lazy. */ WARN_ON(!this_cpu_read(cpu_tlbstate_shared.is_lazy)); switch_mm(NULL, &init_mm, NULL); } EXPORT_SYMBOL_GPL(leave_mm); void switch_mm(struct mm_struct *prev, struct mm_struct *next, struct task_struct *tsk) { unsigned long flags; local_irq_save(flags); switch_mm_irqs_off(NULL, next, tsk); local_irq_restore(flags); } /* * Invoked from return to user/guest by a task that opted-in to L1D * flushing but ended up running on an SMT enabled core due to wrong * affinity settings or CPU hotplug. This is part of the paranoid L1D flush * contract which this task requested. */ static void l1d_flush_force_sigbus(struct callback_head *ch) { force_sig(SIGBUS); } static void l1d_flush_evaluate(unsigned long prev_mm, unsigned long next_mm, struct task_struct *next) { /* Flush L1D if the outgoing task requests it */ if (prev_mm & LAST_USER_MM_L1D_FLUSH) wrmsrq(MSR_IA32_FLUSH_CMD, L1D_FLUSH); /* Check whether the incoming task opted in for L1D flush */ if (likely(!(next_mm & LAST_USER_MM_L1D_FLUSH))) return; /* * Validate that it is not running on an SMT sibling as this would * make the exercise pointless because the siblings share L1D. If * it runs on a SMT sibling, notify it with SIGBUS on return to * user/guest */ if (this_cpu_read(cpu_info.smt_active)) { clear_ti_thread_flag(&next->thread_info, TIF_SPEC_L1D_FLUSH); next->l1d_flush_kill.func = l1d_flush_force_sigbus; task_work_add(next, &next->l1d_flush_kill, TWA_RESUME); } } static unsigned long mm_mangle_tif_spec_bits(struct task_struct *next) { unsigned long next_tif = read_task_thread_flags(next); unsigned long spec_bits = (next_tif >> TIF_SPEC_IB) & LAST_USER_MM_SPEC_MASK; /* * Ensure that the bit shift above works as expected and the two flags * end up in bit 0 and 1. */ BUILD_BUG_ON(TIF_SPEC_L1D_FLUSH != TIF_SPEC_IB + 1); return (unsigned long)next->mm | spec_bits; } static void cond_mitigation(struct task_struct *next) { unsigned long prev_mm, next_mm; if (!next || !next->mm) return; next_mm = mm_mangle_tif_spec_bits(next); prev_mm = this_cpu_read(cpu_tlbstate.last_user_mm_spec); /* * Avoid user->user BTB/RSB poisoning by flushing them when switching * between processes. This stops one process from doing Spectre-v2 * attacks on another. * * Both, the conditional and the always IBPB mode use the mm * pointer to avoid the IBPB when switching between tasks of the * same process. Using the mm pointer instead of mm->context.ctx_id * opens a hypothetical hole vs. mm_struct reuse, which is more or * less impossible to control by an attacker. Aside of that it * would only affect the first schedule so the theoretically * exposed data is not really interesting. */ if (static_branch_likely(&switch_mm_cond_ibpb)) { /* * This is a bit more complex than the always mode because * it has to handle two cases: * * 1) Switch from a user space task (potential attacker) * which has TIF_SPEC_IB set to a user space task * (potential victim) which has TIF_SPEC_IB not set. * * 2) Switch from a user space task (potential attacker) * which has TIF_SPEC_IB not set to a user space task * (potential victim) which has TIF_SPEC_IB set. * * This could be done by unconditionally issuing IBPB when * a task which has TIF_SPEC_IB set is either scheduled in * or out. Though that results in two flushes when: * * - the same user space task is scheduled out and later * scheduled in again and only a kernel thread ran in * between. * * - a user space task belonging to the same process is * scheduled in after a kernel thread ran in between * * - a user space task belonging to the same process is * scheduled in immediately. * * Optimize this with reasonably small overhead for the * above cases. Mangle the TIF_SPEC_IB bit into the mm * pointer of the incoming task which is stored in * cpu_tlbstate.last_user_mm_spec for comparison. * * Issue IBPB only if the mm's are different and one or * both have the IBPB bit set. */ if (next_mm != prev_mm && (next_mm | prev_mm) & LAST_USER_MM_IBPB) indirect_branch_prediction_barrier(); } if (static_branch_unlikely(&switch_mm_always_ibpb)) { /* * Only flush when switching to a user space task with a * different context than the user space task which ran * last on this CPU. */ if ((prev_mm & ~LAST_USER_MM_SPEC_MASK) != (unsigned long)next->mm) indirect_branch_prediction_barrier(); } if (static_branch_unlikely(&switch_mm_cond_l1d_flush)) { /* * Flush L1D when the outgoing task requested it and/or * check whether the incoming task requested L1D flushing * and ended up on an SMT sibling. */ if (unlikely((prev_mm | next_mm) & LAST_USER_MM_L1D_FLUSH)) l1d_flush_evaluate(prev_mm, next_mm, next); } this_cpu_write(cpu_tlbstate.last_user_mm_spec, next_mm); } #ifdef CONFIG_PERF_EVENTS static inline void cr4_update_pce_mm(struct mm_struct *mm) { if (static_branch_unlikely(&rdpmc_always_available_key) || (!static_branch_unlikely(&rdpmc_never_available_key) && atomic_read(&mm->context.perf_rdpmc_allowed))) { /* * Clear the existing dirty counters to * prevent the leak for an RDPMC task. */ perf_clear_dirty_counters(); cr4_set_bits_irqsoff(X86_CR4_PCE); } else cr4_clear_bits_irqsoff(X86_CR4_PCE); } void cr4_update_pce(void *ignored) { cr4_update_pce_mm(this_cpu_read(cpu_tlbstate.loaded_mm)); } #else static inline void cr4_update_pce_mm(struct mm_struct *mm) { } #endif /* * This optimizes when not actually switching mm's. Some architectures use the * 'unused' argument for this optimization, but x86 must use * 'cpu_tlbstate.loaded_mm' instead because it does not always keep * 'current->active_mm' up to date. */ void switch_mm_irqs_off(struct mm_struct *unused, struct mm_struct *next, struct task_struct *tsk) { struct mm_struct *prev = this_cpu_read(cpu_tlbstate.loaded_mm); u16 prev_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid); bool was_lazy = this_cpu_read(cpu_tlbstate_shared.is_lazy); unsigned cpu = smp_processor_id(); unsigned long new_lam; struct new_asid ns; u64 next_tlb_gen; /* We don't want flush_tlb_func() to run concurrently with us. */ if (IS_ENABLED(CONFIG_PROVE_LOCKING)) WARN_ON_ONCE(!irqs_disabled()); /* * Verify that CR3 is what we think it is. This will catch * hypothetical buggy code that directly switches to swapper_pg_dir * without going through leave_mm() / switch_mm_irqs_off() or that * does something like write_cr3(read_cr3_pa()). * * Only do this check if CONFIG_DEBUG_VM=y because __read_cr3() * isn't free. */ #ifdef CONFIG_DEBUG_VM if (WARN_ON_ONCE(__read_cr3() != build_cr3(prev->pgd, prev_asid, tlbstate_lam_cr3_mask()))) { /* * If we were to BUG here, we'd be very likely to kill * the system so hard that we don't see the call trace. * Try to recover instead by ignoring the error and doing * a global flush to minimize the chance of corruption. * * (This is far from being a fully correct recovery. * Architecturally, the CPU could prefetch something * back into an incorrect ASID slot and leave it there * to cause trouble down the road. It's better than * nothing, though.) */ __flush_tlb_all(); } #endif if (was_lazy) this_cpu_write(cpu_tlbstate_shared.is_lazy, false); /* * The membarrier system call requires a full memory barrier and * core serialization before returning to user-space, after * storing to rq->curr, when changing mm. This is because * membarrier() sends IPIs to all CPUs that are in the target mm * to make them issue memory barriers. However, if another CPU * switches to/from the target mm concurrently with * membarrier(), it can cause that CPU not to receive an IPI * when it really should issue a memory barrier. Writing to CR3 * provides that full memory barrier and core serializing * instruction. */ if (prev == next) { /* Not actually switching mm's */ VM_WARN_ON(is_dyn_asid(prev_asid) && this_cpu_read(cpu_tlbstate.ctxs[prev_asid].ctx_id) != next->context.ctx_id); /* * If this races with another thread that enables lam, 'new_lam' * might not match tlbstate_lam_cr3_mask(). */ /* * Even in lazy TLB mode, the CPU should stay set in the * mm_cpumask. The TLB shootdown code can figure out from * cpu_tlbstate_shared.is_lazy whether or not to send an IPI. */ if (IS_ENABLED(CONFIG_DEBUG_VM) && WARN_ON_ONCE(prev != &init_mm && !is_notrack_mm(prev) && !cpumask_test_cpu(cpu, mm_cpumask(next)))) cpumask_set_cpu(cpu, mm_cpumask(next)); /* Check if the current mm is transitioning to a global ASID */ if (mm_needs_global_asid(next, prev_asid)) { next_tlb_gen = atomic64_read(&next->context.tlb_gen); ns = choose_new_asid(next, next_tlb_gen); goto reload_tlb; } /* * Broadcast TLB invalidation keeps this ASID up to date * all the time. */ if (is_global_asid(prev_asid)) return; /* * If the CPU is not in lazy TLB mode, we are just switching * from one thread in a process to another thread in the same * process. No TLB flush required. */ if (!was_lazy) return; /* * Read the tlb_gen to check whether a flush is needed. * If the TLB is up to date, just use it. * The barrier synchronizes with the tlb_gen increment in * the TLB shootdown code. */ smp_mb(); next_tlb_gen = atomic64_read(&next->context.tlb_gen); if (this_cpu_read(cpu_tlbstate.ctxs[prev_asid].tlb_gen) == next_tlb_gen) return; /* * TLB contents went out of date while we were in lazy * mode. Fall through to the TLB switching code below. */ ns.asid = prev_asid; ns.need_flush = true; } else { /* * Apply process to process speculation vulnerability * mitigations if applicable. */ cond_mitigation(tsk); /* * Indicate that CR3 is about to change. nmi_uaccess_okay() * and others are sensitive to the window where mm_cpumask(), * CR3 and cpu_tlbstate.loaded_mm are not all in sync. */ this_cpu_write(cpu_tlbstate.loaded_mm, LOADED_MM_SWITCHING); /* * Make sure this CPU is set in mm_cpumask() such that we'll * receive invalidation IPIs. * * Rely on the smp_mb() implied by cpumask_set_cpu()'s atomic * operation, or explicitly provide one. Such that: * * switch_mm_irqs_off() flush_tlb_mm_range() * smp_store_release(loaded_mm, SWITCHING); atomic64_inc_return(tlb_gen) * smp_mb(); // here // smp_mb() implied * atomic64_read(tlb_gen); this_cpu_read(loaded_mm); * * we properly order against flush_tlb_mm_range(), where the * loaded_mm load can happen in mative_flush_tlb_multi() -> * should_flush_tlb(). * * This way switch_mm() must see the new tlb_gen or * flush_tlb_mm_range() must see the new loaded_mm, or both. */ if (next != &init_mm && !cpumask_test_cpu(cpu, mm_cpumask(next))) cpumask_set_cpu(cpu, mm_cpumask(next)); else smp_mb(); next_tlb_gen = atomic64_read(&next->context.tlb_gen); ns = choose_new_asid(next, next_tlb_gen); } reload_tlb: new_lam = mm_lam_cr3_mask(next); if (ns.need_flush) { VM_WARN_ON_ONCE(is_global_asid(ns.asid)); this_cpu_write(cpu_tlbstate.ctxs[ns.asid].ctx_id, next->context.ctx_id); this_cpu_write(cpu_tlbstate.ctxs[ns.asid].tlb_gen, next_tlb_gen); load_new_mm_cr3(next->pgd, ns.asid, new_lam, true); trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL); } else { /* The new ASID is already up to date. */ load_new_mm_cr3(next->pgd, ns.asid, new_lam, false); trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, 0); } /* Make sure we write CR3 before loaded_mm. */ barrier(); this_cpu_write(cpu_tlbstate.loaded_mm, next); this_cpu_write(cpu_tlbstate.loaded_mm_asid, ns.asid); cpu_tlbstate_update_lam(new_lam, mm_untag_mask(next)); if (next != prev) { cr4_update_pce_mm(next); switch_ldt(prev, next); } } /* * Please ignore the name of this function. It should be called * switch_to_kernel_thread(). * * enter_lazy_tlb() is a hint from the scheduler that we are entering a * kernel thread or other context without an mm. Acceptable implementations * include doing nothing whatsoever, switching to init_mm, or various clever * lazy tricks to try to minimize TLB flushes. * * The scheduler reserves the right to call enter_lazy_tlb() several times * in a row. It will notify us that we're going back to a real mm by * calling switch_mm_irqs_off(). */ void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk) { if (this_cpu_read(cpu_tlbstate.loaded_mm) == &init_mm) return; this_cpu_write(cpu_tlbstate_shared.is_lazy, true); } /* * Using a temporary mm allows to set temporary mappings that are not accessible * by other CPUs. Such mappings are needed to perform sensitive memory writes * that override the kernel memory protections (e.g., W^X), without exposing the * temporary page-table mappings that are required for these write operations to * other CPUs. Using a temporary mm also allows to avoid TLB shootdowns when the * mapping is torn down. Temporary mms can also be used for EFI runtime service * calls or similar functionality. * * It is illegal to schedule while using a temporary mm -- the context switch * code is unaware of the temporary mm and does not know how to context switch. * Use a real (non-temporary) mm in a kernel thread if you need to sleep. * * Note: For sensitive memory writes, the temporary mm needs to be used * exclusively by a single core, and IRQs should be disabled while the * temporary mm is loaded, thereby preventing interrupt handler bugs from * overriding the kernel memory protection. */ struct mm_struct *use_temporary_mm(struct mm_struct *temp_mm) { struct mm_struct *prev_mm; lockdep_assert_preemption_disabled(); guard(irqsave)(); /* * Make sure not to be in TLB lazy mode, as otherwise we'll end up * with a stale address space WITHOUT being in lazy mode after * restoring the previous mm. */ if (this_cpu_read(cpu_tlbstate_shared.is_lazy)) leave_mm(); prev_mm = this_cpu_read(cpu_tlbstate.loaded_mm); switch_mm_irqs_off(NULL, temp_mm, current); /* * If breakpoints are enabled, disable them while the temporary mm is * used. Userspace might set up watchpoints on addresses that are used * in the temporary mm, which would lead to wrong signals being sent or * crashes. * * Note that breakpoints are not disabled selectively, which also causes * kernel breakpoints (e.g., perf's) to be disabled. This might be * undesirable, but still seems reasonable as the code that runs in the * temporary mm should be short. */ if (hw_breakpoint_active()) hw_breakpoint_disable(); return prev_mm; } void unuse_temporary_mm(struct mm_struct *prev_mm) { lockdep_assert_preemption_disabled(); guard(irqsave)(); /* Clear the cpumask, to indicate no TLB flushing is needed anywhere */ cpumask_clear_cpu(smp_processor_id(), mm_cpumask(this_cpu_read(cpu_tlbstate.loaded_mm))); switch_mm_irqs_off(NULL, prev_mm, current); /* * Restore the breakpoints if they were disabled before the temporary mm * was loaded. */ if (hw_breakpoint_active()) hw_breakpoint_restore(); } /* * Call this when reinitializing a CPU. It fixes the following potential * problems: * * - The ASID changed from what cpu_tlbstate thinks it is (most likely * because the CPU was taken down and came back up with CR3's PCID * bits clear. CPU hotplug can do this. * * - The TLB contains junk in slots corresponding to inactive ASIDs. * * - The CPU went so far out to lunch that it may have missed a TLB * flush. */ void initialize_tlbstate_and_flush(void) { int i; struct mm_struct *mm = this_cpu_read(cpu_tlbstate.loaded_mm); u64 tlb_gen = atomic64_read(&init_mm.context.tlb_gen); unsigned long lam = mm_lam_cr3_mask(mm); unsigned long cr3 = __read_cr3(); /* Assert that CR3 already references the right mm. */ WARN_ON((cr3 & CR3_ADDR_MASK) != __pa(mm->pgd)); /* LAM expected to be disabled */ WARN_ON(cr3 & (X86_CR3_LAM_U48 | X86_CR3_LAM_U57)); WARN_ON(lam); /* * Assert that CR4.PCIDE is set if needed. (CR4.PCIDE initialization * doesn't work like other CR4 bits because it can only be set from * long mode.) */ WARN_ON(boot_cpu_has(X86_FEATURE_PCID) && !(cr4_read_shadow() & X86_CR4_PCIDE)); /* Disable LAM, force ASID 0 and force a TLB flush. */ write_cr3(build_cr3(mm->pgd, 0, 0)); /* Reinitialize tlbstate. */ this_cpu_write(cpu_tlbstate.last_user_mm_spec, LAST_USER_MM_INIT); this_cpu_write(cpu_tlbstate.loaded_mm_asid, 0); this_cpu_write(cpu_tlbstate.next_asid, 1); this_cpu_write(cpu_tlbstate.ctxs[0].ctx_id, mm->context.ctx_id); this_cpu_write(cpu_tlbstate.ctxs[0].tlb_gen, tlb_gen); cpu_tlbstate_update_lam(lam, mm_untag_mask(mm)); for (i = 1; i < TLB_NR_DYN_ASIDS; i++) this_cpu_write(cpu_tlbstate.ctxs[i].ctx_id, 0); } /* * flush_tlb_func()'s memory ordering requirement is that any * TLB fills that happen after we flush the TLB are ordered after we * read active_mm's tlb_gen. We don't need any explicit barriers * because all x86 flush operations are serializing and the * atomic64_read operation won't be reordered by the compiler. */ static void flush_tlb_func(void *info) { /* * We have three different tlb_gen values in here. They are: * * - mm_tlb_gen: the latest generation. * - local_tlb_gen: the generation that this CPU has already caught * up to. * - f->new_tlb_gen: the generation that the requester of the flush * wants us to catch up to. */ const struct flush_tlb_info *f = info; struct mm_struct *loaded_mm = this_cpu_read(cpu_tlbstate.loaded_mm); u32 loaded_mm_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid); u64 local_tlb_gen; bool local = smp_processor_id() == f->initiating_cpu; unsigned long nr_invalidate = 0; u64 mm_tlb_gen; /* This code cannot presently handle being reentered. */ VM_WARN_ON(!irqs_disabled()); if (!local) { inc_irq_stat(irq_tlb_count); count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED); } /* The CPU was left in the mm_cpumask of the target mm. Clear it. */ if (f->mm && f->mm != loaded_mm) { cpumask_clear_cpu(raw_smp_processor_id(), mm_cpumask(f->mm)); trace_tlb_flush(TLB_REMOTE_WRONG_CPU, 0); return; } if (unlikely(loaded_mm == &init_mm)) return; /* Reload the ASID if transitioning into or out of a global ASID */ if (mm_needs_global_asid(loaded_mm, loaded_mm_asid)) { switch_mm_irqs_off(NULL, loaded_mm, NULL); loaded_mm_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid); } /* Broadcast ASIDs are always kept up to date with INVLPGB. */ if (is_global_asid(loaded_mm_asid)) return; VM_WARN_ON(this_cpu_read(cpu_tlbstate.ctxs[loaded_mm_asid].ctx_id) != loaded_mm->context.ctx_id); if (this_cpu_read(cpu_tlbstate_shared.is_lazy)) { /* * We're in lazy mode. We need to at least flush our * paging-structure cache to avoid speculatively reading * garbage into our TLB. Since switching to init_mm is barely * slower than a minimal flush, just switch to init_mm. * * This should be rare, with native_flush_tlb_multi() skipping * IPIs to lazy TLB mode CPUs. */ switch_mm_irqs_off(NULL, &init_mm, NULL); return; } local_tlb_gen = this_cpu_read(cpu_tlbstate.ctxs[loaded_mm_asid].tlb_gen); if (unlikely(f->new_tlb_gen != TLB_GENERATION_INVALID && f->new_tlb_gen <= local_tlb_gen)) { /* * The TLB is already up to date in respect to f->new_tlb_gen. * While the core might be still behind mm_tlb_gen, checking * mm_tlb_gen unnecessarily would have negative caching effects * so avoid it. */ return; } /* * Defer mm_tlb_gen reading as long as possible to avoid cache * contention. */ mm_tlb_gen = atomic64_read(&loaded_mm->context.tlb_gen); if (unlikely(local_tlb_gen == mm_tlb_gen)) { /* * There's nothing to do: we're already up to date. This can * happen if two concurrent flushes happen -- the first flush to * be handled can catch us all the way up, leaving no work for * the second flush. */ goto done; } WARN_ON_ONCE(local_tlb_gen > mm_tlb_gen); WARN_ON_ONCE(f->new_tlb_gen > mm_tlb_gen); /* * If we get to this point, we know that our TLB is out of date. * This does not strictly imply that we need to flush (it's * possible that f->new_tlb_gen <= local_tlb_gen), but we're * going to need to flush in the very near future, so we might * as well get it over with. * * The only question is whether to do a full or partial flush. * * We do a partial flush if requested and two extra conditions * are met: * * 1. f->new_tlb_gen == local_tlb_gen + 1. We have an invariant that * we've always done all needed flushes to catch up to * local_tlb_gen. If, for example, local_tlb_gen == 2 and * f->new_tlb_gen == 3, then we know that the flush needed to bring * us up to date for tlb_gen 3 is the partial flush we're * processing. * * As an example of why this check is needed, suppose that there * are two concurrent flushes. The first is a full flush that * changes context.tlb_gen from 1 to 2. The second is a partial * flush that changes context.tlb_gen from 2 to 3. If they get * processed on this CPU in reverse order, we'll see * local_tlb_gen == 1, mm_tlb_gen == 3, and end != TLB_FLUSH_ALL. * If we were to use __flush_tlb_one_user() and set local_tlb_gen to * 3, we'd be break the invariant: we'd update local_tlb_gen above * 1 without the full flush that's needed for tlb_gen 2. * * 2. f->new_tlb_gen == mm_tlb_gen. This is purely an optimization. * Partial TLB flushes are not all that much cheaper than full TLB * flushes, so it seems unlikely that it would be a performance win * to do a partial flush if that won't bring our TLB fully up to * date. By doing a full flush instead, we can increase * local_tlb_gen all the way to mm_tlb_gen and we can probably * avoid another flush in the very near future. */ if (f->end != TLB_FLUSH_ALL && f->new_tlb_gen == local_tlb_gen + 1 && f->new_tlb_gen == mm_tlb_gen) { /* Partial flush */ unsigned long addr = f->start; /* Partial flush cannot have invalid generations */ VM_WARN_ON(f->new_tlb_gen == TLB_GENERATION_INVALID); /* Partial flush must have valid mm */ VM_WARN_ON(f->mm == NULL); nr_invalidate = (f->end - f->start) >> f->stride_shift; while (addr < f->end) { flush_tlb_one_user(addr); addr += 1UL << f->stride_shift; } if (local) count_vm_tlb_events(NR_TLB_LOCAL_FLUSH_ONE, nr_invalidate); } else { /* Full flush. */ nr_invalidate = TLB_FLUSH_ALL; flush_tlb_local(); if (local) count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL); } /* Both paths above update our state to mm_tlb_gen. */ this_cpu_write(cpu_tlbstate.ctxs[loaded_mm_asid].tlb_gen, mm_tlb_gen); /* Tracing is done in a unified manner to reduce the code size */ done: trace_tlb_flush(!local ? TLB_REMOTE_SHOOTDOWN : (f->mm == NULL) ? TLB_LOCAL_SHOOTDOWN : TLB_LOCAL_MM_SHOOTDOWN, nr_invalidate); } static bool should_flush_tlb(int cpu, void *data) { struct mm_struct *loaded_mm = per_cpu(cpu_tlbstate.loaded_mm, cpu); struct flush_tlb_info *info = data; /* * Order the 'loaded_mm' and 'is_lazy' against their * write ordering in switch_mm_irqs_off(). Ensure * 'is_lazy' is at least as new as 'loaded_mm'. */ smp_rmb(); /* Lazy TLB will get flushed at the next context switch. */ if (per_cpu(cpu_tlbstate_shared.is_lazy, cpu)) return false; /* No mm means kernel memory flush. */ if (!info->mm) return true; /* * While switching, the remote CPU could have state from * either the prev or next mm. Assume the worst and flush. */ if (loaded_mm == LOADED_MM_SWITCHING) return true; /* The target mm is loaded, and the CPU is not lazy. */ if (loaded_mm == info->mm) return true; /* In cpumask, but not the loaded mm? Periodically remove by flushing. */ if (info->trim_cpumask) return true; return false; } static bool should_trim_cpumask(struct mm_struct *mm) { if (time_after(jiffies, READ_ONCE(mm->context.next_trim_cpumask))) { WRITE_ONCE(mm->context.next_trim_cpumask, jiffies + HZ); return true; } return false; } DEFINE_PER_CPU_SHARED_ALIGNED(struct tlb_state_shared, cpu_tlbstate_shared); EXPORT_PER_CPU_SYMBOL(cpu_tlbstate_shared); STATIC_NOPV void native_flush_tlb_multi(const struct cpumask *cpumask, const struct flush_tlb_info *info) { /* * Do accounting and tracing. Note that there are (and have always been) * cases in which a remote TLB flush will be traced, but eventually * would not happen. */ count_vm_tlb_event(NR_TLB_REMOTE_FLUSH); if (info->end == TLB_FLUSH_ALL) trace_tlb_flush(TLB_REMOTE_SEND_IPI, TLB_FLUSH_ALL); else trace_tlb_flush(TLB_REMOTE_SEND_IPI, (info->end - info->start) >> PAGE_SHIFT); /* * If no page tables were freed, we can skip sending IPIs to * CPUs in lazy TLB mode. They will flush the CPU themselves * at the next context switch. * * However, if page tables are getting freed, we need to send the * IPI everywhere, to prevent CPUs in lazy TLB mode from tripping * up on the new contents of what used to be page tables, while * doing a speculative memory access. */ if (info->freed_tables || mm_in_asid_transition(info->mm)) on_each_cpu_mask(cpumask, flush_tlb_func, (void *)info, true); else on_each_cpu_cond_mask(should_flush_tlb, flush_tlb_func, (void *)info, 1, cpumask); } void flush_tlb_multi(const struct cpumask *cpumask, const struct flush_tlb_info *info) { __flush_tlb_multi(cpumask, info); } /* * See Documentation/arch/x86/tlb.rst for details. We choose 33 * because it is large enough to cover the vast majority (at * least 95%) of allocations, and is small enough that we are * confident it will not cause too much overhead. Each single * flush is about 100 ns, so this caps the maximum overhead at * _about_ 3,000 ns. * * This is in units of pages. */ unsigned long tlb_single_page_flush_ceiling __read_mostly = 33; static DEFINE_PER_CPU_SHARED_ALIGNED(struct flush_tlb_info, flush_tlb_info); #ifdef CONFIG_DEBUG_VM static DEFINE_PER_CPU(unsigned int, flush_tlb_info_idx); #endif static struct flush_tlb_info *get_flush_tlb_info(struct mm_struct *mm, unsigned long start, unsigned long end, unsigned int stride_shift, bool freed_tables, u64 new_tlb_gen) { struct flush_tlb_info *info = this_cpu_ptr(&flush_tlb_info); #ifdef CONFIG_DEBUG_VM /* * Ensure that the following code is non-reentrant and flush_tlb_info * is not overwritten. This means no TLB flushing is initiated by * interrupt handlers and machine-check exception handlers. */ BUG_ON(this_cpu_inc_return(flush_tlb_info_idx) != 1); #endif /* * If the number of flushes is so large that a full flush * would be faster, do a full flush. */ if ((end - start) >> stride_shift > tlb_single_page_flush_ceiling) { start = 0; end = TLB_FLUSH_ALL; } info->start = start; info->end = end; info->mm = mm; info->stride_shift = stride_shift; info->freed_tables = freed_tables; info->new_tlb_gen = new_tlb_gen; info->initiating_cpu = smp_processor_id(); info->trim_cpumask = 0; return info; } static void put_flush_tlb_info(void) { #ifdef CONFIG_DEBUG_VM /* Complete reentrancy prevention checks */ barrier(); this_cpu_dec(flush_tlb_info_idx); #endif } void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start, unsigned long end, unsigned int stride_shift, bool freed_tables) { struct flush_tlb_info *info; int cpu = get_cpu(); u64 new_tlb_gen; /* This is also a barrier that synchronizes with switch_mm(). */ new_tlb_gen = inc_mm_tlb_gen(mm); info = get_flush_tlb_info(mm, start, end, stride_shift, freed_tables, new_tlb_gen); /* * flush_tlb_multi() is not optimized for the common case in which only * a local TLB flush is needed. Optimize this use-case by calling * flush_tlb_func_local() directly in this case. */ if (mm_global_asid(mm)) { broadcast_tlb_flush(info); } else if (cpumask_any_but(mm_cpumask(mm), cpu) < nr_cpu_ids) { info->trim_cpumask = should_trim_cpumask(mm); flush_tlb_multi(mm_cpumask(mm), info); consider_global_asid(mm); } else if (mm == this_cpu_read(cpu_tlbstate.loaded_mm)) { lockdep_assert_irqs_enabled(); local_irq_disable(); flush_tlb_func(info); local_irq_enable(); } put_flush_tlb_info(); put_cpu(); mmu_notifier_arch_invalidate_secondary_tlbs(mm, start, end); } static void do_flush_tlb_all(void *info) { count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED); __flush_tlb_all(); } void flush_tlb_all(void) { count_vm_tlb_event(NR_TLB_REMOTE_FLUSH); /* First try (faster) hardware-assisted TLB invalidation. */ if (cpu_feature_enabled(X86_FEATURE_INVLPGB)) invlpgb_flush_all(); else /* Fall back to the IPI-based invalidation. */ on_each_cpu(do_flush_tlb_all, NULL, 1); } /* Flush an arbitrarily large range of memory with INVLPGB. */ static void invlpgb_kernel_range_flush(struct flush_tlb_info *info) { unsigned long addr, nr; for (addr = info->start; addr < info->end; addr += nr << PAGE_SHIFT) { nr = (info->end - addr) >> PAGE_SHIFT; /* * INVLPGB has a limit on the size of ranges it can * flush. Break up large flushes. */ nr = clamp_val(nr, 1, invlpgb_count_max); invlpgb_flush_addr_nosync(addr, nr); } __tlbsync(); } static void do_kernel_range_flush(void *info) { struct flush_tlb_info *f = info; unsigned long addr; /* flush range by one by one 'invlpg' */ for (addr = f->start; addr < f->end; addr += PAGE_SIZE) flush_tlb_one_kernel(addr); } static void kernel_tlb_flush_all(struct flush_tlb_info *info) { if (cpu_feature_enabled(X86_FEATURE_INVLPGB)) invlpgb_flush_all(); else on_each_cpu(do_flush_tlb_all, NULL, 1); } static void kernel_tlb_flush_range(struct flush_tlb_info *info) { if (cpu_feature_enabled(X86_FEATURE_INVLPGB)) invlpgb_kernel_range_flush(info); else on_each_cpu(do_kernel_range_flush, info, 1); } void flush_tlb_kernel_range(unsigned long start, unsigned long end) { struct flush_tlb_info *info; guard(preempt)(); info = get_flush_tlb_info(NULL, start, end, PAGE_SHIFT, false, TLB_GENERATION_INVALID); if (info->end == TLB_FLUSH_ALL) kernel_tlb_flush_all(info); else kernel_tlb_flush_range(info); put_flush_tlb_info(); } /* * This can be used from process context to figure out what the value of * CR3 is without needing to do a (slow) __read_cr3(). * * It's intended to be used for code like KVM that sneakily changes CR3 * and needs to restore it. It needs to be used very carefully. */ unsigned long __get_current_cr3_fast(void) { unsigned long cr3 = build_cr3(this_cpu_read(cpu_tlbstate.loaded_mm)->pgd, this_cpu_read(cpu_tlbstate.loaded_mm_asid), tlbstate_lam_cr3_mask()); /* For now, be very restrictive about when this can be called. */ VM_WARN_ON(in_nmi() || preemptible()); VM_BUG_ON(cr3 != __read_cr3()); return cr3; } EXPORT_SYMBOL_FOR_KVM(__get_current_cr3_fast); /* * Flush one page in the kernel mapping */ void flush_tlb_one_kernel(unsigned long addr) { count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ONE); /* * If PTI is off, then __flush_tlb_one_user() is just INVLPG or its * paravirt equivalent. Even with PCID, this is sufficient: we only * use PCID if we also use global PTEs for the kernel mapping, and * INVLPG flushes global translations across all address spaces. * * If PTI is on, then the kernel is mapped with non-global PTEs, and * __flush_tlb_one_user() will flush the given address for the current * kernel address space and for its usermode counterpart, but it does * not flush it for other address spaces. */ flush_tlb_one_user(addr); if (!static_cpu_has(X86_FEATURE_PTI)) return; /* * See above. We need to propagate the flush to all other address * spaces. In principle, we only need to propagate it to kernelmode * address spaces, but the extra bookkeeping we would need is not * worth it. */ this_cpu_write(cpu_tlbstate.invalidate_other, true); } /* * Flush one page in the user mapping */ STATIC_NOPV void native_flush_tlb_one_user(unsigned long addr) { u32 loaded_mm_asid; bool cpu_pcide; /* Flush 'addr' from the kernel PCID: */ invlpg(addr); /* If PTI is off there is no user PCID and nothing to flush. */ if (!static_cpu_has(X86_FEATURE_PTI)) return; loaded_mm_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid); cpu_pcide = this_cpu_read(cpu_tlbstate.cr4) & X86_CR4_PCIDE; /* * invpcid_flush_one(pcid>0) will #GP if CR4.PCIDE==0. Check * 'cpu_pcide' to ensure that *this* CPU will not trigger those * #GP's even if called before CR4.PCIDE has been initialized. */ if (boot_cpu_has(X86_FEATURE_INVPCID) && cpu_pcide) invpcid_flush_one(user_pcid(loaded_mm_asid), addr); else invalidate_user_asid(loaded_mm_asid); } void flush_tlb_one_user(unsigned long addr) { __flush_tlb_one_user(addr); } /* * Flush everything */ STATIC_NOPV void native_flush_tlb_global(void) { unsigned long flags; if (static_cpu_has(X86_FEATURE_INVPCID)) { /* * Using INVPCID is considerably faster than a pair of writes * to CR4 sandwiched inside an IRQ flag save/restore. * * Note, this works with CR4.PCIDE=0 or 1. */ invpcid_flush_all(); return; } /* * Read-modify-write to CR4 - protect it from preemption and * from interrupts. (Use the raw variant because this code can * be called from deep inside debugging code.) */ raw_local_irq_save(flags); __native_tlb_flush_global(this_cpu_read(cpu_tlbstate.cr4)); raw_local_irq_restore(flags); } /* * Flush the entire current user mapping */ STATIC_NOPV void native_flush_tlb_local(void) { /* * Preemption or interrupts must be disabled to protect the access * to the per CPU variable and to prevent being preempted between * read_cr3() and write_cr3(). */ WARN_ON_ONCE(preemptible()); invalidate_user_asid(this_cpu_read(cpu_tlbstate.loaded_mm_asid)); /* If current->mm == NULL then the read_cr3() "borrows" an mm */ native_write_cr3(__native_read_cr3()); } void flush_tlb_local(void) { __flush_tlb_local(); } /* * Flush everything */ void __flush_tlb_all(void) { /* * This is to catch users with enabled preemption and the PGE feature * and don't trigger the warning in __native_flush_tlb(). */ VM_WARN_ON_ONCE(preemptible()); if (cpu_feature_enabled(X86_FEATURE_PGE)) { __flush_tlb_global(); } else { /* * !PGE -> !PCID (setup_pcid()), thus every flush is total. */ flush_tlb_local(); } } EXPORT_SYMBOL_FOR_KVM(__flush_tlb_all); void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch) { struct flush_tlb_info *info; int cpu = get_cpu(); info = get_flush_tlb_info(NULL, 0, TLB_FLUSH_ALL, 0, false, TLB_GENERATION_INVALID); /* * flush_tlb_multi() is not optimized for the common case in which only * a local TLB flush is needed. Optimize this use-case by calling * flush_tlb_func_local() directly in this case. */ if (cpu_feature_enabled(X86_FEATURE_INVLPGB) && batch->unmapped_pages) { invlpgb_flush_all_nonglobals(); batch->unmapped_pages = false; } else if (cpumask_any_but(&batch->cpumask, cpu) < nr_cpu_ids) { flush_tlb_multi(&batch->cpumask, info); } else if (cpumask_test_cpu(cpu, &batch->cpumask)) { lockdep_assert_irqs_enabled(); local_irq_disable(); flush_tlb_func(info); local_irq_enable(); } cpumask_clear(&batch->cpumask); put_flush_tlb_info(); put_cpu(); } /* * Blindly accessing user memory from NMI context can be dangerous * if we're in the middle of switching the current user task or * switching the loaded mm. It can also be dangerous if we * interrupted some kernel code that was temporarily using a * different mm. */ bool nmi_uaccess_okay(void) { struct mm_struct *loaded_mm = this_cpu_read(cpu_tlbstate.loaded_mm); struct mm_struct *current_mm = current->mm; VM_WARN_ON_ONCE(!loaded_mm); /* * The condition we want to check is * current_mm->pgd == __va(read_cr3_pa()). This may be slow, though, * if we're running in a VM with shadow paging, and nmi_uaccess_okay() * is supposed to be reasonably fast. * * Instead, we check the almost equivalent but somewhat conservative * condition below, and we rely on the fact that switch_mm_irqs_off() * sets loaded_mm to LOADED_MM_SWITCHING before writing to CR3. */ if (loaded_mm != current_mm) return false; VM_WARN_ON_ONCE(__pa(current_mm->pgd) != read_cr3_pa()); return true; } static ssize_t tlbflush_read_file(struct file *file, char __user *user_buf, size_t count, loff_t *ppos) { char buf[32]; unsigned int len; len = sprintf(buf, "%ld\n", tlb_single_page_flush_ceiling); return simple_read_from_buffer(user_buf, count, ppos, buf, len); } static ssize_t tlbflush_write_file(struct file *file, const char __user *user_buf, size_t count, loff_t *ppos) { char buf[32]; ssize_t len; int ceiling; len = min(count, sizeof(buf) - 1); if (copy_from_user(buf, user_buf, len)) return -EFAULT; buf[len] = '\0'; if (kstrtoint(buf, 0, &ceiling)) return -EINVAL; if (ceiling < 0) return -EINVAL; tlb_single_page_flush_ceiling = ceiling; return count; } static const struct file_operations fops_tlbflush = { .read = tlbflush_read_file, .write = tlbflush_write_file, .llseek = default_llseek, }; static int __init create_tlb_single_page_flush_ceiling(void) { debugfs_create_file("tlb_single_page_flush_ceiling", S_IRUSR | S_IWUSR, arch_debugfs_dir, NULL, &fops_tlbflush); return 0; } late_initcall(create_tlb_single_page_flush_ceiling);
