// SPDX-License-Identifier: GPL-2.0

#include <linux/spinlock.h>
#include <linux/percpu.h>
#include <linux/kallsyms.h>
#include <linux/kcore.h>
#include <linux/pgtable.h>

#include <asm/cpu_entry_area.h>
#include <asm/fixmap.h>
#include <asm/desc.h>
#include <asm/kasan.h>
#include <asm/setup.h>

static DEFINE_PER_CPU_PAGE_ALIGNED(struct entry_stack_page, entry_stack_storage);

#ifdef CONFIG_X86_64
static DEFINE_PER_CPU_PAGE_ALIGNED(struct exception_stacks, exception_stacks);
DEFINE_PER_CPU(struct cea_exception_stacks*, cea_exception_stacks);

static DEFINE_PER_CPU_READ_MOSTLY(unsigned long, _cea_offset);

static __always_inline unsigned int cea_offset(unsigned int cpu)
{
        return per_cpu(_cea_offset, cpu);
}

static __init void init_cea_offsets(void)
{
        unsigned int max_cea;
        unsigned int i, j;

        if (!kaslr_enabled()) {
                for_each_possible_cpu(i)
                        per_cpu(_cea_offset, i) = i;
                return;
        }

        max_cea = (CPU_ENTRY_AREA_MAP_SIZE - PAGE_SIZE) / CPU_ENTRY_AREA_SIZE;

        /* O(sodding terrible) */
        for_each_possible_cpu(i) {
                unsigned int cea;

again:
                cea = get_random_u32_below(max_cea);

                for_each_possible_cpu(j) {
                        if (cea_offset(j) == cea)
                                goto again;

                        if (i == j)
                                break;
                }

                per_cpu(_cea_offset, i) = cea;
        }
}
#else /* !X86_64 */
DECLARE_PER_CPU_PAGE_ALIGNED(struct doublefault_stack, doublefault_stack);

static __always_inline unsigned int cea_offset(unsigned int cpu)
{
        return cpu;
}
static inline void init_cea_offsets(void) { }
#endif

/* Is called from entry code, so must be noinstr */
noinstr struct cpu_entry_area *get_cpu_entry_area(int cpu)
{
        unsigned long va = CPU_ENTRY_AREA_PER_CPU + cea_offset(cpu) * CPU_ENTRY_AREA_SIZE;
        BUILD_BUG_ON(sizeof(struct cpu_entry_area) % PAGE_SIZE != 0);

        return (struct cpu_entry_area *) va;
}
EXPORT_SYMBOL(get_cpu_entry_area);

void cea_set_pte(void *cea_vaddr, phys_addr_t pa, pgprot_t flags)
{
        unsigned long va = (unsigned long) cea_vaddr;
        pte_t pte = pfn_pte(pa >> PAGE_SHIFT, flags);

        /*
         * The cpu_entry_area is shared between the user and kernel
         * page tables.  All of its ptes can safely be global.
         * _PAGE_GLOBAL gets reused to help indicate PROT_NONE for
         * non-present PTEs, so be careful not to set it in that
         * case to avoid confusion.
         */
        if (boot_cpu_has(X86_FEATURE_PGE) &&
            (pgprot_val(flags) & _PAGE_PRESENT))
                pte = pte_set_flags(pte, _PAGE_GLOBAL);

        set_pte_vaddr(va, pte);
}

static void __init
cea_map_percpu_pages(void *cea_vaddr, void *ptr, int pages, pgprot_t prot)
{
        for ( ; pages; pages--, cea_vaddr+= PAGE_SIZE, ptr += PAGE_SIZE)
                cea_set_pte(cea_vaddr, per_cpu_ptr_to_phys(ptr), prot);
}

static void __init percpu_setup_debug_store(unsigned int cpu)
{
#ifdef CONFIG_CPU_SUP_INTEL
        unsigned int npages;
        void *cea;

        if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
                return;

        cea = &get_cpu_entry_area(cpu)->cpu_debug_store;
        npages = sizeof(struct debug_store) / PAGE_SIZE;
        BUILD_BUG_ON(sizeof(struct debug_store) % PAGE_SIZE != 0);
        cea_map_percpu_pages(cea, &per_cpu(cpu_debug_store, cpu), npages,
                             PAGE_KERNEL);

        cea = &get_cpu_entry_area(cpu)->cpu_debug_buffers;
        /*
         * Force the population of PMDs for not yet allocated per cpu
         * memory like debug store buffers.
         */
        npages = sizeof(struct debug_store_buffers) / PAGE_SIZE;
        for (; npages; npages--, cea += PAGE_SIZE)
                cea_set_pte(cea, 0, PAGE_NONE);
#endif
}

#ifdef CONFIG_X86_64

#define cea_map_stack(name) do {                                        \
        npages = sizeof(estacks->name## _stack) / PAGE_SIZE;            \
        cea_map_percpu_pages(cea->estacks.name## _stack,                \
                        estacks->name## _stack, npages, PAGE_KERNEL);   \
        } while (0)

static void __init percpu_setup_exception_stacks(unsigned int cpu)
{
        struct exception_stacks *estacks = per_cpu_ptr(&exception_stacks, cpu);
        struct cpu_entry_area *cea = get_cpu_entry_area(cpu);
        unsigned int npages;

        BUILD_BUG_ON(sizeof(exception_stacks) % PAGE_SIZE != 0);

        per_cpu(cea_exception_stacks, cpu) = &cea->estacks;

        /*
         * The exceptions stack mappings in the per cpu area are protected
         * by guard pages so each stack must be mapped separately. DB2 is
         * not mapped; it just exists to catch triple nesting of #DB.
         */
        cea_map_stack(DF);
        cea_map_stack(NMI);
        cea_map_stack(DB);
        cea_map_stack(MCE);

        if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT)) {
                if (cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT)) {
                        cea_map_stack(VC);
                        cea_map_stack(VC2);
                }
        }
}
#else
static void __init percpu_setup_exception_stacks(unsigned int cpu)
{
        struct cpu_entry_area *cea = get_cpu_entry_area(cpu);

        cea_map_percpu_pages(&cea->doublefault_stack,
                             &per_cpu(doublefault_stack, cpu), 1, PAGE_KERNEL);
}
#endif

/* Setup the fixmap mappings only once per-processor */
static void __init setup_cpu_entry_area(unsigned int cpu)
{
        struct cpu_entry_area *cea = get_cpu_entry_area(cpu);
#ifdef CONFIG_X86_64
        /* On 64-bit systems, we use a read-only fixmap GDT and TSS. */
        pgprot_t gdt_prot = PAGE_KERNEL_RO;
        pgprot_t tss_prot = PAGE_KERNEL_RO;
#else
        /*
         * On 32-bit systems, the GDT cannot be read-only because
         * our double fault handler uses a task gate, and entering through
         * a task gate needs to change an available TSS to busy.  If the
         * GDT is read-only, that will triple fault.  The TSS cannot be
         * read-only because the CPU writes to it on task switches.
         */
        pgprot_t gdt_prot = PAGE_KERNEL;
        pgprot_t tss_prot = PAGE_KERNEL;
#endif

        kasan_populate_shadow_for_vaddr(cea, CPU_ENTRY_AREA_SIZE,
                                        early_cpu_to_node(cpu));

        cea_set_pte(&cea->gdt, get_cpu_gdt_paddr(cpu), gdt_prot);

        cea_map_percpu_pages(&cea->entry_stack_page,
                             per_cpu_ptr(&entry_stack_storage, cpu), 1,
                             PAGE_KERNEL);

        /*
         * The Intel SDM says (Volume 3, 7.2.1):
         *
         *  Avoid placing a page boundary in the part of the TSS that the
         *  processor reads during a task switch (the first 104 bytes). The
         *  processor may not correctly perform address translations if a
         *  boundary occurs in this area. During a task switch, the processor
         *  reads and writes into the first 104 bytes of each TSS (using
         *  contiguous physical addresses beginning with the physical address
         *  of the first byte of the TSS). So, after TSS access begins, if
         *  part of the 104 bytes is not physically contiguous, the processor
         *  will access incorrect information without generating a page-fault
         *  exception.
         *
         * There are also a lot of errata involving the TSS spanning a page
         * boundary.  Assert that we're not doing that.
         */
        BUILD_BUG_ON((offsetof(struct tss_struct, x86_tss) ^
                      offsetofend(struct tss_struct, x86_tss)) & PAGE_MASK);
        BUILD_BUG_ON(sizeof(struct tss_struct) % PAGE_SIZE != 0);
        /*
         * VMX changes the host TR limit to 0x67 after a VM exit. This is
         * okay, since 0x67 covers the size of struct x86_hw_tss. Make sure
         * that this is correct.
         */
        BUILD_BUG_ON(offsetof(struct tss_struct, x86_tss) != 0);
        BUILD_BUG_ON(sizeof(struct x86_hw_tss) != 0x68);

        cea_map_percpu_pages(&cea->tss, &per_cpu(cpu_tss_rw, cpu),
                             sizeof(struct tss_struct) / PAGE_SIZE, tss_prot);

#ifdef CONFIG_X86_32
        per_cpu(cpu_entry_area, cpu) = cea;
#endif

        percpu_setup_exception_stacks(cpu);

        percpu_setup_debug_store(cpu);
}

static __init void setup_cpu_entry_area_ptes(void)
{
#ifdef CONFIG_X86_32
        unsigned long start, end;

        /* The +1 is for the readonly IDT: */
        BUILD_BUG_ON((CPU_ENTRY_AREA_PAGES+1)*PAGE_SIZE != CPU_ENTRY_AREA_MAP_SIZE);
        BUG_ON(CPU_ENTRY_AREA_BASE & ~PMD_MASK);

        start = CPU_ENTRY_AREA_BASE;
        end = start + CPU_ENTRY_AREA_MAP_SIZE;

        /* Careful here: start + PMD_SIZE might wrap around */
        for (; start < end && start >= CPU_ENTRY_AREA_BASE; start += PMD_SIZE)
                populate_extra_pte(start);
#endif
}

void __init setup_cpu_entry_areas(void)
{
        unsigned int cpu;

        init_cea_offsets();

        setup_cpu_entry_area_ptes();

        for_each_possible_cpu(cpu)
                setup_cpu_entry_area(cpu);

        /*
         * This is the last essential update to swapper_pgdir which needs
         * to be synchronized to initial_page_table on 32bit.
         */
        sync_initial_page_table();
}