// SPDX-License-Identifier: GPL-2.0-only
/*
 * KVM dirty ring implementation
 *
 * Copyright 2019 Red Hat, Inc.
 */
#include <linux/kvm_host.h>
#include <linux/kvm.h>
#include <linux/vmalloc.h>
#include <linux/kvm_dirty_ring.h>
#include <trace/events/kvm.h>
#include "kvm_mm.h"

int __weak kvm_cpu_dirty_log_size(struct kvm *kvm)
{
        return 0;
}

u32 kvm_dirty_ring_get_rsvd_entries(struct kvm *kvm)
{
        return KVM_DIRTY_RING_RSVD_ENTRIES + kvm_cpu_dirty_log_size(kvm);
}

bool kvm_use_dirty_bitmap(struct kvm *kvm)
{
        lockdep_assert_held(&kvm->slots_lock);

        return !kvm->dirty_ring_size || kvm->dirty_ring_with_bitmap;
}

#ifndef CONFIG_NEED_KVM_DIRTY_RING_WITH_BITMAP
bool kvm_arch_allow_write_without_running_vcpu(struct kvm *kvm)
{
        return false;
}
#endif

static u32 kvm_dirty_ring_used(struct kvm_dirty_ring *ring)
{
        return READ_ONCE(ring->dirty_index) - READ_ONCE(ring->reset_index);
}

static bool kvm_dirty_ring_soft_full(struct kvm_dirty_ring *ring)
{
        return kvm_dirty_ring_used(ring) >= ring->soft_limit;
}

static bool kvm_dirty_ring_full(struct kvm_dirty_ring *ring)
{
        return kvm_dirty_ring_used(ring) >= ring->size;
}

static void kvm_reset_dirty_gfn(struct kvm *kvm, u32 slot, u64 offset, u64 mask)
{
        struct kvm_memory_slot *memslot;
        int as_id, id;

        as_id = slot >> 16;
        id = (u16)slot;

        if (as_id >= kvm_arch_nr_memslot_as_ids(kvm) || id >= KVM_USER_MEM_SLOTS)
                return;

        memslot = id_to_memslot(__kvm_memslots(kvm, as_id), id);

        if (!memslot || (offset + __fls(mask)) >= memslot->npages)
                return;

        KVM_MMU_LOCK(kvm);
        kvm_arch_mmu_enable_log_dirty_pt_masked(kvm, memslot, offset, mask);
        KVM_MMU_UNLOCK(kvm);
}

int kvm_dirty_ring_alloc(struct kvm *kvm, struct kvm_dirty_ring *ring,
                         int index, u32 size)
{
        ring->dirty_gfns = vzalloc(size);
        if (!ring->dirty_gfns)
                return -ENOMEM;

        ring->size = size / sizeof(struct kvm_dirty_gfn);
        ring->soft_limit = ring->size - kvm_dirty_ring_get_rsvd_entries(kvm);
        ring->dirty_index = 0;
        ring->reset_index = 0;
        ring->index = index;

        return 0;
}

static inline void kvm_dirty_gfn_set_invalid(struct kvm_dirty_gfn *gfn)
{
        smp_store_release(&gfn->flags, 0);
}

static inline void kvm_dirty_gfn_set_dirtied(struct kvm_dirty_gfn *gfn)
{
        gfn->flags = KVM_DIRTY_GFN_F_DIRTY;
}

static inline bool kvm_dirty_gfn_harvested(struct kvm_dirty_gfn *gfn)
{
        return smp_load_acquire(&gfn->flags) & KVM_DIRTY_GFN_F_RESET;
}

int kvm_dirty_ring_reset(struct kvm *kvm, struct kvm_dirty_ring *ring,
                         int *nr_entries_reset)
{
        /*
         * To minimize mmu_lock contention, batch resets for harvested entries
         * whose gfns are in the same slot, and are within N frame numbers of
         * each other, where N is the number of bits in an unsigned long.  For
         * simplicity, process the current set of entries when the next entry
         * can't be included in the batch.
         *
         * Track the current batch slot, the gfn offset into the slot for the
         * batch, and the bitmask of gfns that need to be reset (relative to
         * offset).  Note, the offset may be adjusted backwards, e.g. so that
         * a sequence of gfns X, X-1, ... X-N-1 can be batched.
         */
        u32 cur_slot, next_slot;
        u64 cur_offset, next_offset;
        unsigned long mask = 0;
        struct kvm_dirty_gfn *entry;

        /*
         * Ensure concurrent calls to KVM_RESET_DIRTY_RINGS are serialized,
         * e.g. so that KVM fully resets all entries processed by a given call
         * before returning to userspace.  Holding slots_lock also protects
         * the various memslot accesses.
         */
        lockdep_assert_held(&kvm->slots_lock);

        while (likely((*nr_entries_reset) < INT_MAX)) {
                if (signal_pending(current))
                        return -EINTR;

                entry = &ring->dirty_gfns[ring->reset_index & (ring->size - 1)];

                if (!kvm_dirty_gfn_harvested(entry))
                        break;

                next_slot = READ_ONCE(entry->slot);
                next_offset = READ_ONCE(entry->offset);

                /* Update the flags to reflect that this GFN is reset */
                kvm_dirty_gfn_set_invalid(entry);

                ring->reset_index++;
                (*nr_entries_reset)++;

                if (mask) {
                        /*
                         * While the size of each ring is fixed, it's possible
                         * for the ring to be constantly re-dirtied/harvested
                         * while the reset is in-progress (the hard limit exists
                         * only to guard against the count becoming negative).
                         */
                        cond_resched();

                        /*
                         * Try to coalesce the reset operations when the guest
                         * is scanning pages in the same slot.
                         */
                        if (next_slot == cur_slot) {
                                s64 delta = next_offset - cur_offset;

                                if (delta >= 0 && delta < BITS_PER_LONG) {
                                        mask |= 1ull << delta;
                                        continue;
                                }

                                /* Backwards visit, careful about overflows! */
                                if (delta > -BITS_PER_LONG && delta < 0 &&
                                (mask << -delta >> -delta) == mask) {
                                        cur_offset = next_offset;
                                        mask = (mask << -delta) | 1;
                                        continue;
                                }
                        }

                        /*
                         * Reset the slot for all the harvested entries that
                         * have been gathered, but not yet fully processed.
                         */
                        kvm_reset_dirty_gfn(kvm, cur_slot, cur_offset, mask);
                }

                /*
                 * The current slot was reset or this is the first harvested
                 * entry, (re)initialize the metadata.
                 */
                cur_slot = next_slot;
                cur_offset = next_offset;
                mask = 1;
        }

        /*
         * Perform a final reset if there are harvested entries that haven't
         * been processed, which is guaranteed if at least one harvested was
         * found.  The loop only performs a reset when the "next" entry can't
         * be batched with the "current" entry(s), and that reset processes the
         * _current_ entry(s); i.e. the last harvested entry, a.k.a. next, will
         * always be left pending.
         */
        if (mask)
                kvm_reset_dirty_gfn(kvm, cur_slot, cur_offset, mask);

        /*
         * The request KVM_REQ_DIRTY_RING_SOFT_FULL will be cleared
         * by the VCPU thread next time when it enters the guest.
         */

        trace_kvm_dirty_ring_reset(ring);

        return 0;
}

void kvm_dirty_ring_push(struct kvm_vcpu *vcpu, u32 slot, u64 offset)
{
        struct kvm_dirty_ring *ring = &vcpu->dirty_ring;
        struct kvm_dirty_gfn *entry;

        /* It should never get full */
        WARN_ON_ONCE(kvm_dirty_ring_full(ring));

        entry = &ring->dirty_gfns[ring->dirty_index & (ring->size - 1)];

        entry->slot = slot;
        entry->offset = offset;
        /*
         * Make sure the data is filled in before we publish this to
         * the userspace program.  There's no paired kernel-side reader.
         */
        smp_wmb();
        kvm_dirty_gfn_set_dirtied(entry);
        ring->dirty_index++;
        trace_kvm_dirty_ring_push(ring, slot, offset);

        if (kvm_dirty_ring_soft_full(ring))
                kvm_make_request(KVM_REQ_DIRTY_RING_SOFT_FULL, vcpu);
}

bool kvm_dirty_ring_check_request(struct kvm_vcpu *vcpu)
{
        /*
         * The VCPU isn't runnable when the dirty ring becomes soft full.
         * The KVM_REQ_DIRTY_RING_SOFT_FULL event is always set to prevent
         * the VCPU from running until the dirty pages are harvested and
         * the dirty ring is reset by userspace.
         */
        if (kvm_check_request(KVM_REQ_DIRTY_RING_SOFT_FULL, vcpu) &&
            kvm_dirty_ring_soft_full(&vcpu->dirty_ring)) {
                kvm_make_request(KVM_REQ_DIRTY_RING_SOFT_FULL, vcpu);
                vcpu->run->exit_reason = KVM_EXIT_DIRTY_RING_FULL;
                trace_kvm_dirty_ring_exit(vcpu);
                return true;
        }

        return false;
}

struct page *kvm_dirty_ring_get_page(struct kvm_dirty_ring *ring, u32 offset)
{
        return vmalloc_to_page((void *)ring->dirty_gfns + offset * PAGE_SIZE);
}

void kvm_dirty_ring_free(struct kvm_dirty_ring *ring)
{
        vfree(ring->dirty_gfns);
        ring->dirty_gfns = NULL;
}