/*
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * KVM/MIPS MMU handling in the KVM module.
 *
 * Copyright (C) 2012  MIPS Technologies, Inc.  All rights reserved.
 * Authors: Sanjay Lal <sanjayl@kymasys.com>
 */

#include <linux/highmem.h>
#include <linux/kvm_host.h>
#include <linux/uaccess.h>
#include <asm/mmu_context.h>
#include <asm/pgalloc.h>

/*
 * KVM_MMU_CACHE_MIN_PAGES is the number of GPA page table translation levels
 * for which pages need to be cached.
 */
#if defined(__PAGETABLE_PMD_FOLDED)
#define KVM_MMU_CACHE_MIN_PAGES 1
#else
#define KVM_MMU_CACHE_MIN_PAGES 2
#endif

static int mmu_topup_memory_cache(struct kvm_mmu_memory_cache *cache,
                                  int min, int max)
{
        void *page;

        BUG_ON(max > KVM_NR_MEM_OBJS);
        if (cache->nobjs >= min)
                return 0;
        while (cache->nobjs < max) {
                page = (void *)__get_free_page(GFP_KERNEL);
                if (!page)
                        return -ENOMEM;
                cache->objects[cache->nobjs++] = page;
        }
        return 0;
}

static void mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc)
{
        while (mc->nobjs)
                free_page((unsigned long)mc->objects[--mc->nobjs]);
}

static void *mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc)
{
        void *p;

        BUG_ON(!mc || !mc->nobjs);
        p = mc->objects[--mc->nobjs];
        return p;
}

void kvm_mmu_free_memory_caches(struct kvm_vcpu *vcpu)
{
        mmu_free_memory_cache(&vcpu->arch.mmu_page_cache);
}

/**
 * kvm_pgd_init() - Initialise KVM GPA page directory.
 * @page:       Pointer to page directory (PGD) for KVM GPA.
 *
 * Initialise a KVM GPA page directory with pointers to the invalid table, i.e.
 * representing no mappings. This is similar to pgd_init(), however it
 * initialises all the page directory pointers, not just the ones corresponding
 * to the userland address space (since it is for the guest physical address
 * space rather than a virtual address space).
 */
static void kvm_pgd_init(void *page)
{
        unsigned long *p, *end;
        unsigned long entry;

#ifdef __PAGETABLE_PMD_FOLDED
        entry = (unsigned long)invalid_pte_table;
#else
        entry = (unsigned long)invalid_pmd_table;
#endif

        p = (unsigned long *)page;
        end = p + PTRS_PER_PGD;

        do {
                p[0] = entry;
                p[1] = entry;
                p[2] = entry;
                p[3] = entry;
                p[4] = entry;
                p += 8;
                p[-3] = entry;
                p[-2] = entry;
                p[-1] = entry;
        } while (p != end);
}

/**
 * kvm_pgd_alloc() - Allocate and initialise a KVM GPA page directory.
 *
 * Allocate a blank KVM GPA page directory (PGD) for representing guest physical
 * to host physical page mappings.
 *
 * Returns:     Pointer to new KVM GPA page directory.
 *              NULL on allocation failure.
 */
pgd_t *kvm_pgd_alloc(void)
{
        pgd_t *ret;

        ret = (pgd_t *)__get_free_pages(GFP_KERNEL, PGD_ORDER);
        if (ret)
                kvm_pgd_init(ret);

        return ret;
}

/**
 * kvm_mips_walk_pgd() - Walk page table with optional allocation.
 * @pgd:        Page directory pointer.
 * @addr:       Address to index page table using.
 * @cache:      MMU page cache to allocate new page tables from, or NULL.
 *
 * Walk the page tables pointed to by @pgd to find the PTE corresponding to the
 * address @addr. If page tables don't exist for @addr, they will be created
 * from the MMU cache if @cache is not NULL.
 *
 * Returns:     Pointer to pte_t corresponding to @addr.
 *              NULL if a page table doesn't exist for @addr and !@cache.
 *              NULL if a page table allocation failed.
 */
static pte_t *kvm_mips_walk_pgd(pgd_t *pgd, struct kvm_mmu_memory_cache *cache,
                                unsigned long addr)
{
        p4d_t *p4d;
        pud_t *pud;
        pmd_t *pmd;

        pgd += pgd_index(addr);
        if (pgd_none(*pgd)) {
                /* Not used on MIPS yet */
                BUG();
                return NULL;
        }
        p4d = p4d_offset(pgd, addr);
        pud = pud_offset(p4d, addr);
        if (pud_none(*pud)) {
                pmd_t *new_pmd;

                if (!cache)
                        return NULL;
                new_pmd = mmu_memory_cache_alloc(cache);
                pmd_init((unsigned long)new_pmd,
                         (unsigned long)invalid_pte_table);
                pud_populate(NULL, pud, new_pmd);
        }
        pmd = pmd_offset(pud, addr);
        if (pmd_none(*pmd)) {
                pte_t *new_pte;

                if (!cache)
                        return NULL;
                new_pte = mmu_memory_cache_alloc(cache);
                clear_page(new_pte);
                pmd_populate_kernel(NULL, pmd, new_pte);
        }
        return pte_offset(pmd, addr);
}

/* Caller must hold kvm->mm_lock */
static pte_t *kvm_mips_pte_for_gpa(struct kvm *kvm,
                                   struct kvm_mmu_memory_cache *cache,
                                   unsigned long addr)
{
        return kvm_mips_walk_pgd(kvm->arch.gpa_mm.pgd, cache, addr);
}

/*
 * kvm_mips_flush_gpa_{pte,pmd,pud,pgd,pt}.
 * Flush a range of guest physical address space from the VM's GPA page tables.
 */

static bool kvm_mips_flush_gpa_pte(pte_t *pte, unsigned long start_gpa,
                                   unsigned long end_gpa)
{
        int i_min = __pte_offset(start_gpa);
        int i_max = __pte_offset(end_gpa);
        bool safe_to_remove = (i_min == 0 && i_max == PTRS_PER_PTE - 1);
        int i;

        for (i = i_min; i <= i_max; ++i) {
                if (!pte_present(pte[i]))
                        continue;

                set_pte(pte + i, __pte(0));
        }
        return safe_to_remove;
}

static bool kvm_mips_flush_gpa_pmd(pmd_t *pmd, unsigned long start_gpa,
                                   unsigned long end_gpa)
{
        pte_t *pte;
        unsigned long end = ~0ul;
        int i_min = pmd_index(start_gpa);
        int i_max = pmd_index(end_gpa);
        bool safe_to_remove = (i_min == 0 && i_max == PTRS_PER_PMD - 1);
        int i;

        for (i = i_min; i <= i_max; ++i, start_gpa = 0) {
                if (!pmd_present(pmd[i]))
                        continue;

                pte = pte_offset(pmd + i, 0);
                if (i == i_max)
                        end = end_gpa;

                if (kvm_mips_flush_gpa_pte(pte, start_gpa, end)) {
                        pmd_clear(pmd + i);
                        pte_free_kernel(NULL, pte);
                } else {
                        safe_to_remove = false;
                }
        }
        return safe_to_remove;
}

static bool kvm_mips_flush_gpa_pud(pud_t *pud, unsigned long start_gpa,
                                   unsigned long end_gpa)
{
        pmd_t *pmd;
        unsigned long end = ~0ul;
        int i_min = pud_index(start_gpa);
        int i_max = pud_index(end_gpa);
        bool safe_to_remove = (i_min == 0 && i_max == PTRS_PER_PUD - 1);
        int i;

        for (i = i_min; i <= i_max; ++i, start_gpa = 0) {
                if (!pud_present(pud[i]))
                        continue;

                pmd = pmd_offset(pud + i, 0);
                if (i == i_max)
                        end = end_gpa;

                if (kvm_mips_flush_gpa_pmd(pmd, start_gpa, end)) {
                        pud_clear(pud + i);
                        pmd_free(NULL, pmd);
                } else {
                        safe_to_remove = false;
                }
        }
        return safe_to_remove;
}

static bool kvm_mips_flush_gpa_pgd(pgd_t *pgd, unsigned long start_gpa,
                                   unsigned long end_gpa)
{
        p4d_t *p4d;
        pud_t *pud;
        unsigned long end = ~0ul;
        int i_min = pgd_index(start_gpa);
        int i_max = pgd_index(end_gpa);
        bool safe_to_remove = (i_min == 0 && i_max == PTRS_PER_PGD - 1);
        int i;

        for (i = i_min; i <= i_max; ++i, start_gpa = 0) {
                if (!pgd_present(pgd[i]))
                        continue;

                p4d = p4d_offset(pgd, 0);
                pud = pud_offset(p4d + i, 0);
                if (i == i_max)
                        end = end_gpa;

                if (kvm_mips_flush_gpa_pud(pud, start_gpa, end)) {
                        pgd_clear(pgd + i);
                        pud_free(NULL, pud);
                } else {
                        safe_to_remove = false;
                }
        }
        return safe_to_remove;
}

/**
 * kvm_mips_flush_gpa_pt() - Flush a range of guest physical addresses.
 * @kvm:        KVM pointer.
 * @start_gfn:  Guest frame number of first page in GPA range to flush.
 * @end_gfn:    Guest frame number of last page in GPA range to flush.
 *
 * Flushes a range of GPA mappings from the GPA page tables.
 *
 * The caller must hold the @kvm->mmu_lock spinlock.
 *
 * Returns:     Whether its safe to remove the top level page directory because
 *              all lower levels have been removed.
 */
bool kvm_mips_flush_gpa_pt(struct kvm *kvm, gfn_t start_gfn, gfn_t end_gfn)
{
        return kvm_mips_flush_gpa_pgd(kvm->arch.gpa_mm.pgd,
                                      start_gfn << PAGE_SHIFT,
                                      end_gfn << PAGE_SHIFT);
}

#define BUILD_PTE_RANGE_OP(name, op)                                    \
static int kvm_mips_##name##_pte(pte_t *pte, unsigned long start,       \
                                 unsigned long end)                     \
{                                                                       \
        int ret = 0;                                                    \
        int i_min = __pte_offset(start);                                \
        int i_max = __pte_offset(end);                                  \
        int i;                                                          \
        pte_t old, new;                                                 \
                                                                        \
        for (i = i_min; i <= i_max; ++i) {                              \
                if (!pte_present(pte[i]))                               \
                        continue;                                       \
                                                                        \
                old = pte[i];                                           \
                new = op(old);                                          \
                if (pte_val(new) == pte_val(old))                       \
                        continue;                                       \
                set_pte(pte + i, new);                                  \
                ret = 1;                                                \
        }                                                               \
        return ret;                                                     \
}                                                                       \
                                                                        \
/* returns true if anything was done */                                 \
static int kvm_mips_##name##_pmd(pmd_t *pmd, unsigned long start,       \
                                 unsigned long end)                     \
{                                                                       \
        int ret = 0;                                                    \
        pte_t *pte;                                                     \
        unsigned long cur_end = ~0ul;                                   \
        int i_min = pmd_index(start);                           \
        int i_max = pmd_index(end);                                     \
        int i;                                                          \
                                                                        \
        for (i = i_min; i <= i_max; ++i, start = 0) {                   \
                if (!pmd_present(pmd[i]))                               \
                        continue;                                       \
                                                                        \
                pte = pte_offset(pmd + i, 0);                           \
                if (i == i_max)                                         \
                        cur_end = end;                                  \
                                                                        \
                ret |= kvm_mips_##name##_pte(pte, start, cur_end);      \
        }                                                               \
        return ret;                                                     \
}                                                                       \
                                                                        \
static int kvm_mips_##name##_pud(pud_t *pud, unsigned long start,       \
                                 unsigned long end)                     \
{                                                                       \
        int ret = 0;                                                    \
        pmd_t *pmd;                                                     \
        unsigned long cur_end = ~0ul;                                   \
        int i_min = pud_index(start);                           \
        int i_max = pud_index(end);                                     \
        int i;                                                          \
                                                                        \
        for (i = i_min; i <= i_max; ++i, start = 0) {                   \
                if (!pud_present(pud[i]))                               \
                        continue;                                       \
                                                                        \
                pmd = pmd_offset(pud + i, 0);                           \
                if (i == i_max)                                         \
                        cur_end = end;                                  \
                                                                        \
                ret |= kvm_mips_##name##_pmd(pmd, start, cur_end);      \
        }                                                               \
        return ret;                                                     \
}                                                                       \
                                                                        \
static int kvm_mips_##name##_pgd(pgd_t *pgd, unsigned long start,       \
                                 unsigned long end)                     \
{                                                                       \
        int ret = 0;                                                    \
        p4d_t *p4d;                                                     \
        pud_t *pud;                                                     \
        unsigned long cur_end = ~0ul;                                   \
        int i_min = pgd_index(start);                                   \
        int i_max = pgd_index(end);                                     \
        int i;                                                          \
                                                                        \
        for (i = i_min; i <= i_max; ++i, start = 0) {                   \
                if (!pgd_present(pgd[i]))                               \
                        continue;                                       \
                                                                        \
                p4d = p4d_offset(pgd, 0);                               \
                pud = pud_offset(p4d + i, 0);                           \
                if (i == i_max)                                         \
                        cur_end = end;                                  \
                                                                        \
                ret |= kvm_mips_##name##_pud(pud, start, cur_end);      \
        }                                                               \
        return ret;                                                     \
}

/*
 * kvm_mips_mkclean_gpa_pt.
 * Mark a range of guest physical address space clean (writes fault) in the VM's
 * GPA page table to allow dirty page tracking.
 */

BUILD_PTE_RANGE_OP(mkclean, pte_mkclean)

/**
 * kvm_mips_mkclean_gpa_pt() - Make a range of guest physical addresses clean.
 * @kvm:        KVM pointer.
 * @start_gfn:  Guest frame number of first page in GPA range to flush.
 * @end_gfn:    Guest frame number of last page in GPA range to flush.
 *
 * Make a range of GPA mappings clean so that guest writes will fault and
 * trigger dirty page logging.
 *
 * The caller must hold the @kvm->mmu_lock spinlock.
 *
 * Returns:     Whether any GPA mappings were modified, which would require
 *              derived mappings (GVA page tables & TLB enties) to be
 *              invalidated.
 */
int kvm_mips_mkclean_gpa_pt(struct kvm *kvm, gfn_t start_gfn, gfn_t end_gfn)
{
        return kvm_mips_mkclean_pgd(kvm->arch.gpa_mm.pgd,
                                    start_gfn << PAGE_SHIFT,
                                    end_gfn << PAGE_SHIFT);
}

/**
 * kvm_arch_mmu_enable_log_dirty_pt_masked() - write protect dirty pages
 * @kvm:        The KVM pointer
 * @slot:       The memory slot associated with mask
 * @gfn_offset: The gfn offset in memory slot
 * @mask:       The mask of dirty pages at offset 'gfn_offset' in this memory
 *              slot to be write protected
 *
 * Walks bits set in mask write protects the associated pte's. Caller must
 * acquire @kvm->mmu_lock.
 */
void kvm_arch_mmu_enable_log_dirty_pt_masked(struct kvm *kvm,
                struct kvm_memory_slot *slot,
                gfn_t gfn_offset, unsigned long mask)
{
        gfn_t base_gfn = slot->base_gfn + gfn_offset;
        gfn_t start = base_gfn +  __ffs(mask);
        gfn_t end = base_gfn + __fls(mask);

        kvm_mips_mkclean_gpa_pt(kvm, start, end);
}

/*
 * kvm_mips_mkold_gpa_pt.
 * Mark a range of guest physical address space old (all accesses fault) in the
 * VM's GPA page table to allow detection of commonly used pages.
 */

BUILD_PTE_RANGE_OP(mkold, pte_mkold)

static int kvm_mips_mkold_gpa_pt(struct kvm *kvm, gfn_t start_gfn,
                                 gfn_t end_gfn)
{
        return kvm_mips_mkold_pgd(kvm->arch.gpa_mm.pgd,
                                  start_gfn << PAGE_SHIFT,
                                  end_gfn << PAGE_SHIFT);
}

static int handle_hva_to_gpa(struct kvm *kvm,
                             unsigned long start,
                             unsigned long end,
                             int (*handler)(struct kvm *kvm, gfn_t gfn,
                                            gpa_t gfn_end,
                                            struct kvm_memory_slot *memslot,
                                            void *data),
                             void *data)
{
        struct kvm_memslots *slots;
        struct kvm_memory_slot *memslot;
        int ret = 0;

        slots = kvm_memslots(kvm);

        /* we only care about the pages that the guest sees */
        kvm_for_each_memslot(memslot, slots) {
                unsigned long hva_start, hva_end;
                gfn_t gfn, gfn_end;

                hva_start = max(start, memslot->userspace_addr);
                hva_end = min(end, memslot->userspace_addr +
                                        (memslot->npages << PAGE_SHIFT));
                if (hva_start >= hva_end)
                        continue;

                /*
                 * {gfn(page) | page intersects with [hva_start, hva_end)} =
                 * {gfn_start, gfn_start+1, ..., gfn_end-1}.
                 */
                gfn = hva_to_gfn_memslot(hva_start, memslot);
                gfn_end = hva_to_gfn_memslot(hva_end + PAGE_SIZE - 1, memslot);

                ret |= handler(kvm, gfn, gfn_end, memslot, data);
        }

        return ret;
}


static int kvm_unmap_hva_handler(struct kvm *kvm, gfn_t gfn, gfn_t gfn_end,
                                 struct kvm_memory_slot *memslot, void *data)
{
        kvm_mips_flush_gpa_pt(kvm, gfn, gfn_end);
        return 1;
}

int kvm_unmap_hva_range(struct kvm *kvm, unsigned long start, unsigned long end)
{
        handle_hva_to_gpa(kvm, start, end, &kvm_unmap_hva_handler, NULL);

        kvm_mips_callbacks->flush_shadow_all(kvm);
        return 0;
}

static int kvm_set_spte_handler(struct kvm *kvm, gfn_t gfn, gfn_t gfn_end,
                                struct kvm_memory_slot *memslot, void *data)
{
        gpa_t gpa = gfn << PAGE_SHIFT;
        pte_t hva_pte = *(pte_t *)data;
        pte_t *gpa_pte = kvm_mips_pte_for_gpa(kvm, NULL, gpa);
        pte_t old_pte;

        if (!gpa_pte)
                return 0;

        /* Mapping may need adjusting depending on memslot flags */
        old_pte = *gpa_pte;
        if (memslot->flags & KVM_MEM_LOG_DIRTY_PAGES && !pte_dirty(old_pte))
                hva_pte = pte_mkclean(hva_pte);
        else if (memslot->flags & KVM_MEM_READONLY)
                hva_pte = pte_wrprotect(hva_pte);

        set_pte(gpa_pte, hva_pte);

        /* Replacing an absent or old page doesn't need flushes */
        if (!pte_present(old_pte) || !pte_young(old_pte))
                return 0;

        /* Pages swapped, aged, moved, or cleaned require flushes */
        return !pte_present(hva_pte) ||
               !pte_young(hva_pte) ||
               pte_pfn(old_pte) != pte_pfn(hva_pte) ||
               (pte_dirty(old_pte) && !pte_dirty(hva_pte));
}

int kvm_set_spte_hva(struct kvm *kvm, unsigned long hva, pte_t pte)
{
        unsigned long end = hva + PAGE_SIZE;
        int ret;

        ret = handle_hva_to_gpa(kvm, hva, end, &kvm_set_spte_handler, &pte);
        if (ret)
                kvm_mips_callbacks->flush_shadow_all(kvm);
        return 0;
}

static int kvm_age_hva_handler(struct kvm *kvm, gfn_t gfn, gfn_t gfn_end,
                               struct kvm_memory_slot *memslot, void *data)
{
        return kvm_mips_mkold_gpa_pt(kvm, gfn, gfn_end);
}

static int kvm_test_age_hva_handler(struct kvm *kvm, gfn_t gfn, gfn_t gfn_end,
                                    struct kvm_memory_slot *memslot, void *data)
{
        gpa_t gpa = gfn << PAGE_SHIFT;
        pte_t *gpa_pte = kvm_mips_pte_for_gpa(kvm, NULL, gpa);

        if (!gpa_pte)
                return 0;
        return pte_young(*gpa_pte);
}

int kvm_age_hva(struct kvm *kvm, unsigned long start, unsigned long end)
{
        return handle_hva_to_gpa(kvm, start, end, kvm_age_hva_handler, NULL);
}

int kvm_test_age_hva(struct kvm *kvm, unsigned long hva)
{
        return handle_hva_to_gpa(kvm, hva, hva, kvm_test_age_hva_handler, NULL);
}

/**
 * _kvm_mips_map_page_fast() - Fast path GPA fault handler.
 * @vcpu:               VCPU pointer.
 * @gpa:                Guest physical address of fault.
 * @write_fault:        Whether the fault was due to a write.
 * @out_entry:          New PTE for @gpa (written on success unless NULL).
 * @out_buddy:          New PTE for @gpa's buddy (written on success unless
 *                      NULL).
 *
 * Perform fast path GPA fault handling, doing all that can be done without
 * calling into KVM. This handles marking old pages young (for idle page
 * tracking), and dirtying of clean pages (for dirty page logging).
 *
 * Returns:     0 on success, in which case we can update derived mappings and
 *              resume guest execution.
 *              -EFAULT on failure due to absent GPA mapping or write to
 *              read-only page, in which case KVM must be consulted.
 */
static int _kvm_mips_map_page_fast(struct kvm_vcpu *vcpu, unsigned long gpa,
                                   bool write_fault,
                                   pte_t *out_entry, pte_t *out_buddy)
{
        struct kvm *kvm = vcpu->kvm;
        gfn_t gfn = gpa >> PAGE_SHIFT;
        pte_t *ptep;
        kvm_pfn_t pfn = 0;      /* silence bogus GCC warning */
        bool pfn_valid = false;
        int ret = 0;

        spin_lock(&kvm->mmu_lock);

        /* Fast path - just check GPA page table for an existing entry */
        ptep = kvm_mips_pte_for_gpa(kvm, NULL, gpa);
        if (!ptep || !pte_present(*ptep)) {
                ret = -EFAULT;
                goto out;
        }

        /* Track access to pages marked old */
        if (!pte_young(*ptep)) {
                set_pte(ptep, pte_mkyoung(*ptep));
                pfn = pte_pfn(*ptep);
                pfn_valid = true;
                /* call kvm_set_pfn_accessed() after unlock */
        }
        if (write_fault && !pte_dirty(*ptep)) {
                if (!pte_write(*ptep)) {
                        ret = -EFAULT;
                        goto out;
                }

                /* Track dirtying of writeable pages */
                set_pte(ptep, pte_mkdirty(*ptep));
                pfn = pte_pfn(*ptep);
                mark_page_dirty(kvm, gfn);
                kvm_set_pfn_dirty(pfn);
        }

        if (out_entry)
                *out_entry = *ptep;
        if (out_buddy)
                *out_buddy = *ptep_buddy(ptep);

out:
        spin_unlock(&kvm->mmu_lock);
        if (pfn_valid)
                kvm_set_pfn_accessed(pfn);
        return ret;
}

/**
 * kvm_mips_map_page() - Map a guest physical page.
 * @vcpu:               VCPU pointer.
 * @gpa:                Guest physical address of fault.
 * @write_fault:        Whether the fault was due to a write.
 * @out_entry:          New PTE for @gpa (written on success unless NULL).
 * @out_buddy:          New PTE for @gpa's buddy (written on success unless
 *                      NULL).
 *
 * Handle GPA faults by creating a new GPA mapping (or updating an existing
 * one).
 *
 * This takes care of marking pages young or dirty (idle/dirty page tracking),
 * asking KVM for the corresponding PFN, and creating a mapping in the GPA page
 * tables. Derived mappings (GVA page tables and TLBs) must be handled by the
 * caller.
 *
 * Returns:     0 on success, in which case the caller may use the @out_entry
 *              and @out_buddy PTEs to update derived mappings and resume guest
 *              execution.
 *              -EFAULT if there is no memory region at @gpa or a write was
 *              attempted to a read-only memory region. This is usually handled
 *              as an MMIO access.
 */
static int kvm_mips_map_page(struct kvm_vcpu *vcpu, unsigned long gpa,
                             bool write_fault,
                             pte_t *out_entry, pte_t *out_buddy)
{
        struct kvm *kvm = vcpu->kvm;
        struct kvm_mmu_memory_cache *memcache = &vcpu->arch.mmu_page_cache;
        gfn_t gfn = gpa >> PAGE_SHIFT;
        int srcu_idx, err;
        kvm_pfn_t pfn;
        pte_t *ptep, entry, old_pte;
        bool writeable;
        unsigned long prot_bits;
        unsigned long mmu_seq;

        /* Try the fast path to handle old / clean pages */
        srcu_idx = srcu_read_lock(&kvm->srcu);
        err = _kvm_mips_map_page_fast(vcpu, gpa, write_fault, out_entry,
                                      out_buddy);
        if (!err)
                goto out;

        /* We need a minimum of cached pages ready for page table creation */
        err = mmu_topup_memory_cache(memcache, KVM_MMU_CACHE_MIN_PAGES,
                                     KVM_NR_MEM_OBJS);
        if (err)
                goto out;

retry:
        /*
         * Used to check for invalidations in progress, of the pfn that is
         * returned by pfn_to_pfn_prot below.
         */
        mmu_seq = kvm->mmu_notifier_seq;
        /*
         * Ensure the read of mmu_notifier_seq isn't reordered with PTE reads in
         * gfn_to_pfn_prot() (which calls get_user_pages()), so that we don't
         * risk the page we get a reference to getting unmapped before we have a
         * chance to grab the mmu_lock without mmu_notifier_retry() noticing.
         *
         * This smp_rmb() pairs with the effective smp_wmb() of the combination
         * of the pte_unmap_unlock() after the PTE is zapped, and the
         * spin_lock() in kvm_mmu_notifier_invalidate_<page|range_end>() before
         * mmu_notifier_seq is incremented.
         */
        smp_rmb();

        /* Slow path - ask KVM core whether we can access this GPA */
        pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, &writeable);
        if (is_error_noslot_pfn(pfn)) {
                err = -EFAULT;
                goto out;
        }

        spin_lock(&kvm->mmu_lock);
        /* Check if an invalidation has taken place since we got pfn */
        if (mmu_notifier_retry(kvm, mmu_seq)) {
                /*
                 * This can happen when mappings are changed asynchronously, but
                 * also synchronously if a COW is triggered by
                 * gfn_to_pfn_prot().
                 */
                spin_unlock(&kvm->mmu_lock);
                kvm_release_pfn_clean(pfn);
                goto retry;
        }

        /* Ensure page tables are allocated */
        ptep = kvm_mips_pte_for_gpa(kvm, memcache, gpa);

        /* Set up the PTE */
        prot_bits = _PAGE_PRESENT | __READABLE | _page_cachable_default;
        if (writeable) {
                prot_bits |= _PAGE_WRITE;
                if (write_fault) {
                        prot_bits |= __WRITEABLE;
                        mark_page_dirty(kvm, gfn);
                        kvm_set_pfn_dirty(pfn);
                }
        }
        entry = pfn_pte(pfn, __pgprot(prot_bits));

        /* Write the PTE */
        old_pte = *ptep;
        set_pte(ptep, entry);

        err = 0;
        if (out_entry)
                *out_entry = *ptep;
        if (out_buddy)
                *out_buddy = *ptep_buddy(ptep);

        spin_unlock(&kvm->mmu_lock);
        kvm_release_pfn_clean(pfn);
        kvm_set_pfn_accessed(pfn);
out:
        srcu_read_unlock(&kvm->srcu, srcu_idx);
        return err;
}

static pte_t *kvm_trap_emul_pte_for_gva(struct kvm_vcpu *vcpu,
                                        unsigned long addr)
{
        struct kvm_mmu_memory_cache *memcache = &vcpu->arch.mmu_page_cache;
        pgd_t *pgdp;
        int ret;

        /* We need a minimum of cached pages ready for page table creation */
        ret = mmu_topup_memory_cache(memcache, KVM_MMU_CACHE_MIN_PAGES,
                                     KVM_NR_MEM_OBJS);
        if (ret)
                return NULL;

        if (KVM_GUEST_KERNEL_MODE(vcpu))
                pgdp = vcpu->arch.guest_kernel_mm.pgd;
        else
                pgdp = vcpu->arch.guest_user_mm.pgd;

        return kvm_mips_walk_pgd(pgdp, memcache, addr);
}

void kvm_trap_emul_invalidate_gva(struct kvm_vcpu *vcpu, unsigned long addr,
                                  bool user)
{
        pgd_t *pgdp;
        pte_t *ptep;

        addr &= PAGE_MASK << 1;

        pgdp = vcpu->arch.guest_kernel_mm.pgd;
        ptep = kvm_mips_walk_pgd(pgdp, NULL, addr);
        if (ptep) {
                ptep[0] = pfn_pte(0, __pgprot(0));
                ptep[1] = pfn_pte(0, __pgprot(0));
        }

        if (user) {
                pgdp = vcpu->arch.guest_user_mm.pgd;
                ptep = kvm_mips_walk_pgd(pgdp, NULL, addr);
                if (ptep) {
                        ptep[0] = pfn_pte(0, __pgprot(0));
                        ptep[1] = pfn_pte(0, __pgprot(0));
                }
        }
}

/*
 * kvm_mips_flush_gva_{pte,pmd,pud,pgd,pt}.
 * Flush a range of guest physical address space from the VM's GPA page tables.
 */

static bool kvm_mips_flush_gva_pte(pte_t *pte, unsigned long start_gva,
                                   unsigned long end_gva)
{
        int i_min = __pte_offset(start_gva);
        int i_max = __pte_offset(end_gva);
        bool safe_to_remove = (i_min == 0 && i_max == PTRS_PER_PTE - 1);
        int i;

        /*
         * There's no freeing to do, so there's no point clearing individual
         * entries unless only part of the last level page table needs flushing.
         */
        if (safe_to_remove)
                return true;

        for (i = i_min; i <= i_max; ++i) {
                if (!pte_present(pte[i]))
                        continue;

                set_pte(pte + i, __pte(0));
        }
        return false;
}

static bool kvm_mips_flush_gva_pmd(pmd_t *pmd, unsigned long start_gva,
                                   unsigned long end_gva)
{
        pte_t *pte;
        unsigned long end = ~0ul;
        int i_min = pmd_index(start_gva);
        int i_max = pmd_index(end_gva);
        bool safe_to_remove = (i_min == 0 && i_max == PTRS_PER_PMD - 1);
        int i;

        for (i = i_min; i <= i_max; ++i, start_gva = 0) {
                if (!pmd_present(pmd[i]))
                        continue;

                pte = pte_offset(pmd + i, 0);
                if (i == i_max)
                        end = end_gva;

                if (kvm_mips_flush_gva_pte(pte, start_gva, end)) {
                        pmd_clear(pmd + i);
                        pte_free_kernel(NULL, pte);
                } else {
                        safe_to_remove = false;
                }
        }
        return safe_to_remove;
}

static bool kvm_mips_flush_gva_pud(pud_t *pud, unsigned long start_gva,
                                   unsigned long end_gva)
{
        pmd_t *pmd;
        unsigned long end = ~0ul;
        int i_min = pud_index(start_gva);
        int i_max = pud_index(end_gva);
        bool safe_to_remove = (i_min == 0 && i_max == PTRS_PER_PUD - 1);
        int i;

        for (i = i_min; i <= i_max; ++i, start_gva = 0) {
                if (!pud_present(pud[i]))
                        continue;

                pmd = pmd_offset(pud + i, 0);
                if (i == i_max)
                        end = end_gva;

                if (kvm_mips_flush_gva_pmd(pmd, start_gva, end)) {
                        pud_clear(pud + i);
                        pmd_free(NULL, pmd);
                } else {
                        safe_to_remove = false;
                }
        }
        return safe_to_remove;
}

static bool kvm_mips_flush_gva_pgd(pgd_t *pgd, unsigned long start_gva,
                                   unsigned long end_gva)
{
        p4d_t *p4d;
        pud_t *pud;
        unsigned long end = ~0ul;
        int i_min = pgd_index(start_gva);
        int i_max = pgd_index(end_gva);
        bool safe_to_remove = (i_min == 0 && i_max == PTRS_PER_PGD - 1);
        int i;

        for (i = i_min; i <= i_max; ++i, start_gva = 0) {
                if (!pgd_present(pgd[i]))
                        continue;

                p4d = p4d_offset(pgd, 0);
                pud = pud_offset(p4d + i, 0);
                if (i == i_max)
                        end = end_gva;

                if (kvm_mips_flush_gva_pud(pud, start_gva, end)) {
                        pgd_clear(pgd + i);
                        pud_free(NULL, pud);
                } else {
                        safe_to_remove = false;
                }
        }
        return safe_to_remove;
}

void kvm_mips_flush_gva_pt(pgd_t *pgd, enum kvm_mips_flush flags)
{
        if (flags & KMF_GPA) {
                /* all of guest virtual address space could be affected */
                if (flags & KMF_KERN)
                        /* useg, kseg0, seg2/3 */
                        kvm_mips_flush_gva_pgd(pgd, 0, 0x7fffffff);
                else
                        /* useg */
                        kvm_mips_flush_gva_pgd(pgd, 0, 0x3fffffff);
        } else {
                /* useg */
                kvm_mips_flush_gva_pgd(pgd, 0, 0x3fffffff);

                /* kseg2/3 */
                if (flags & KMF_KERN)
                        kvm_mips_flush_gva_pgd(pgd, 0x60000000, 0x7fffffff);
        }
}

static pte_t kvm_mips_gpa_pte_to_gva_unmapped(pte_t pte)
{
        /*
         * Don't leak writeable but clean entries from GPA page tables. We don't
         * want the normal Linux tlbmod handler to handle dirtying when KVM
         * accesses guest memory.
         */
        if (!pte_dirty(pte))
                pte = pte_wrprotect(pte);

        return pte;
}

static pte_t kvm_mips_gpa_pte_to_gva_mapped(pte_t pte, long entrylo)
{
        /* Guest EntryLo overrides host EntryLo */
        if (!(entrylo & ENTRYLO_D))
                pte = pte_mkclean(pte);

        return kvm_mips_gpa_pte_to_gva_unmapped(pte);
}

#ifdef CONFIG_KVM_MIPS_VZ
int kvm_mips_handle_vz_root_tlb_fault(unsigned long badvaddr,
                                      struct kvm_vcpu *vcpu,
                                      bool write_fault)
{
        int ret;

        ret = kvm_mips_map_page(vcpu, badvaddr, write_fault, NULL, NULL);
        if (ret)
                return ret;

        /* Invalidate this entry in the TLB */
        return kvm_vz_host_tlb_inv(vcpu, badvaddr);
}
#endif

/* XXXKYMA: Must be called with interrupts disabled */
int kvm_mips_handle_kseg0_tlb_fault(unsigned long badvaddr,
                                    struct kvm_vcpu *vcpu,
                                    bool write_fault)
{
        unsigned long gpa;
        pte_t pte_gpa[2], *ptep_gva;
        int idx;

        if (KVM_GUEST_KSEGX(badvaddr) != KVM_GUEST_KSEG0) {
                kvm_err("%s: Invalid BadVaddr: %#lx\n", __func__, badvaddr);
                kvm_mips_dump_host_tlbs();
                return -1;
        }

        /* Get the GPA page table entry */
        gpa = KVM_GUEST_CPHYSADDR(badvaddr);
        idx = (badvaddr >> PAGE_SHIFT) & 1;
        if (kvm_mips_map_page(vcpu, gpa, write_fault, &pte_gpa[idx],
                              &pte_gpa[!idx]) < 0)
                return -1;

        /* Get the GVA page table entry */
        ptep_gva = kvm_trap_emul_pte_for_gva(vcpu, badvaddr & ~PAGE_SIZE);
        if (!ptep_gva) {
                kvm_err("No ptep for gva %lx\n", badvaddr);
                return -1;
        }

        /* Copy a pair of entries from GPA page table to GVA page table */
        ptep_gva[0] = kvm_mips_gpa_pte_to_gva_unmapped(pte_gpa[0]);
        ptep_gva[1] = kvm_mips_gpa_pte_to_gva_unmapped(pte_gpa[1]);

        /* Invalidate this entry in the TLB, guest kernel ASID only */
        kvm_mips_host_tlb_inv(vcpu, badvaddr, false, true);
        return 0;
}

int kvm_mips_handle_mapped_seg_tlb_fault(struct kvm_vcpu *vcpu,
                                         struct kvm_mips_tlb *tlb,
                                         unsigned long gva,
                                         bool write_fault)
{
        struct kvm *kvm = vcpu->kvm;
        long tlb_lo[2];
        pte_t pte_gpa[2], *ptep_buddy, *ptep_gva;
        unsigned int idx = TLB_LO_IDX(*tlb, gva);
        bool kernel = KVM_GUEST_KERNEL_MODE(vcpu);

        tlb_lo[0] = tlb->tlb_lo[0];
        tlb_lo[1] = tlb->tlb_lo[1];

        /*
         * The commpage address must not be mapped to anything else if the guest
         * TLB contains entries nearby, or commpage accesses will break.
         */
        if (!((gva ^ KVM_GUEST_COMMPAGE_ADDR) & VPN2_MASK & (PAGE_MASK << 1)))
                tlb_lo[TLB_LO_IDX(*tlb, KVM_GUEST_COMMPAGE_ADDR)] = 0;

        /* Get the GPA page table entry */
        if (kvm_mips_map_page(vcpu, mips3_tlbpfn_to_paddr(tlb_lo[idx]),
                              write_fault, &pte_gpa[idx], NULL) < 0)
                return -1;

        /* And its GVA buddy's GPA page table entry if it also exists */
        pte_gpa[!idx] = pfn_pte(0, __pgprot(0));
        if (tlb_lo[!idx] & ENTRYLO_V) {
                spin_lock(&kvm->mmu_lock);
                ptep_buddy = kvm_mips_pte_for_gpa(kvm, NULL,
                                        mips3_tlbpfn_to_paddr(tlb_lo[!idx]));
                if (ptep_buddy)
                        pte_gpa[!idx] = *ptep_buddy;
                spin_unlock(&kvm->mmu_lock);
        }

        /* Get the GVA page table entry pair */
        ptep_gva = kvm_trap_emul_pte_for_gva(vcpu, gva & ~PAGE_SIZE);
        if (!ptep_gva) {
                kvm_err("No ptep for gva %lx\n", gva);
                return -1;
        }

        /* Copy a pair of entries from GPA page table to GVA page table */
        ptep_gva[0] = kvm_mips_gpa_pte_to_gva_mapped(pte_gpa[0], tlb_lo[0]);
        ptep_gva[1] = kvm_mips_gpa_pte_to_gva_mapped(pte_gpa[1], tlb_lo[1]);

        /* Invalidate this entry in the TLB, current guest mode ASID only */
        kvm_mips_host_tlb_inv(vcpu, gva, !kernel, kernel);

        kvm_debug("@ %#lx tlb_lo0: 0x%08lx tlb_lo1: 0x%08lx\n", vcpu->arch.pc,
                  tlb->tlb_lo[0], tlb->tlb_lo[1]);

        return 0;
}

int kvm_mips_handle_commpage_tlb_fault(unsigned long badvaddr,
                                       struct kvm_vcpu *vcpu)
{
        kvm_pfn_t pfn;
        pte_t *ptep;

        ptep = kvm_trap_emul_pte_for_gva(vcpu, badvaddr);
        if (!ptep) {
                kvm_err("No ptep for commpage %lx\n", badvaddr);
                return -1;
        }

        pfn = PFN_DOWN(virt_to_phys(vcpu->arch.kseg0_commpage));
        /* Also set valid and dirty, so refill handler doesn't have to */
        *ptep = pte_mkyoung(pte_mkdirty(pfn_pte(pfn, PAGE_SHARED)));

        /* Invalidate this entry in the TLB, guest kernel ASID only */
        kvm_mips_host_tlb_inv(vcpu, badvaddr, false, true);
        return 0;
}

/**
 * kvm_mips_migrate_count() - Migrate timer.
 * @vcpu:       Virtual CPU.
 *
 * Migrate CP0_Count hrtimer to the current CPU by cancelling and restarting it
 * if it was running prior to being cancelled.
 *
 * Must be called when the VCPU is migrated to a different CPU to ensure that
 * timer expiry during guest execution interrupts the guest and causes the
 * interrupt to be delivered in a timely manner.
 */
static void kvm_mips_migrate_count(struct kvm_vcpu *vcpu)
{
        if (hrtimer_cancel(&vcpu->arch.comparecount_timer))
                hrtimer_restart(&vcpu->arch.comparecount_timer);
}

/* Restore ASID once we are scheduled back after preemption */
void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
{
        unsigned long flags;

        kvm_debug("%s: vcpu %p, cpu: %d\n", __func__, vcpu, cpu);

        local_irq_save(flags);

        vcpu->cpu = cpu;
        if (vcpu->arch.last_sched_cpu != cpu) {
                kvm_debug("[%d->%d]KVM VCPU[%d] switch\n",
                          vcpu->arch.last_sched_cpu, cpu, vcpu->vcpu_id);
                /*
                 * Migrate the timer interrupt to the current CPU so that it
                 * always interrupts the guest and synchronously triggers a
                 * guest timer interrupt.
                 */
                kvm_mips_migrate_count(vcpu);
        }

        /* restore guest state to registers */
        kvm_mips_callbacks->vcpu_load(vcpu, cpu);

        local_irq_restore(flags);
}

/* ASID can change if another task is scheduled during preemption */
void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
{
        unsigned long flags;
        int cpu;

        local_irq_save(flags);

        cpu = smp_processor_id();
        vcpu->arch.last_sched_cpu = cpu;
        vcpu->cpu = -1;

        /* save guest state in registers */
        kvm_mips_callbacks->vcpu_put(vcpu, cpu);

        local_irq_restore(flags);
}

/**
 * kvm_trap_emul_gva_fault() - Safely attempt to handle a GVA access fault.
 * @vcpu:       Virtual CPU.
 * @gva:        Guest virtual address to be accessed.
 * @write:      True if write attempted (must be dirtied and made writable).
 *
 * Safely attempt to handle a GVA fault, mapping GVA pages if necessary, and
 * dirtying the page if @write so that guest instructions can be modified.
 *
 * Returns:     KVM_MIPS_MAPPED on success.
 *              KVM_MIPS_GVA if bad guest virtual address.
 *              KVM_MIPS_GPA if bad guest physical address.
 *              KVM_MIPS_TLB if guest TLB not present.
 *              KVM_MIPS_TLBINV if guest TLB present but not valid.
 *              KVM_MIPS_TLBMOD if guest TLB read only.
 */
enum kvm_mips_fault_result kvm_trap_emul_gva_fault(struct kvm_vcpu *vcpu,
                                                   unsigned long gva,
                                                   bool write)
{
        struct mips_coproc *cop0 = vcpu->arch.cop0;
        struct kvm_mips_tlb *tlb;
        int index;

        if (KVM_GUEST_KSEGX(gva) == KVM_GUEST_KSEG0) {
                if (kvm_mips_handle_kseg0_tlb_fault(gva, vcpu, write) < 0)
                        return KVM_MIPS_GPA;
        } else if ((KVM_GUEST_KSEGX(gva) < KVM_GUEST_KSEG0) ||
                   KVM_GUEST_KSEGX(gva) == KVM_GUEST_KSEG23) {
                /* Address should be in the guest TLB */
                index = kvm_mips_guest_tlb_lookup(vcpu, (gva & VPN2_MASK) |
                          (kvm_read_c0_guest_entryhi(cop0) & KVM_ENTRYHI_ASID));
                if (index < 0)
                        return KVM_MIPS_TLB;
                tlb = &vcpu->arch.guest_tlb[index];

                /* Entry should be valid, and dirty for writes */
                if (!TLB_IS_VALID(*tlb, gva))
                        return KVM_MIPS_TLBINV;
                if (write && !TLB_IS_DIRTY(*tlb, gva))
                        return KVM_MIPS_TLBMOD;

                if (kvm_mips_handle_mapped_seg_tlb_fault(vcpu, tlb, gva, write))
                        return KVM_MIPS_GPA;
        } else {
                return KVM_MIPS_GVA;
        }

        return KVM_MIPS_MAPPED;
}

int kvm_get_inst(u32 *opc, struct kvm_vcpu *vcpu, u32 *out)
{
        int err;

        if (WARN(IS_ENABLED(CONFIG_KVM_MIPS_VZ),
                 "Expect BadInstr/BadInstrP registers to be used with VZ\n"))
                return -EINVAL;

retry:
        kvm_trap_emul_gva_lockless_begin(vcpu);
        err = get_user(*out, opc);
        kvm_trap_emul_gva_lockless_end(vcpu);

        if (unlikely(err)) {
                /*
                 * Try to handle the fault, maybe we just raced with a GVA
                 * invalidation.
                 */
                err = kvm_trap_emul_gva_fault(vcpu, (unsigned long)opc,
                                              false);
                if (unlikely(err)) {
                        kvm_err("%s: illegal address: %p\n",
                                __func__, opc);
                        return -EFAULT;
                }

                /* Hopefully it'll work now */
                goto retry;
        }
        return 0;
}