KVM: x86: remove unused variable from walk_addr_generic()

[deliverable/linux.git] / arch / x86 / kvm / paging_tmpl.h

/*
 * Kernel-based Virtual Machine driver for Linux
 *
 * This module enables machines with Intel VT-x extensions to run virtual
 * machines without emulation or binary translation.
 *
 * MMU support
 *
 * Copyright (C) 2006 Qumranet, Inc.
 * Copyright 2010 Red Hat, Inc. and/or its affiliates.
 *
 * Authors:
 *   Yaniv Kamay  <yaniv@qumranet.com>
 *   Avi Kivity   <avi@qumranet.com>
 *
 * This work is licensed under the terms of the GNU GPL, version 2.  See
 * the COPYING file in the top-level directory.
 *
 */

/*
 * We need the mmu code to access both 32-bit and 64-bit guest ptes,
 * so the code in this file is compiled twice, once per pte size.
 */

#if PTTYPE == 64
        #define pt_element_t u64
        #define guest_walker guest_walker64
        #define FNAME(name) paging##64_##name
        #define PT_BASE_ADDR_MASK PT64_BASE_ADDR_MASK
        #define PT_LVL_ADDR_MASK(lvl) PT64_LVL_ADDR_MASK(lvl)
        #define PT_LVL_OFFSET_MASK(lvl) PT64_LVL_OFFSET_MASK(lvl)
        #define PT_INDEX(addr, level) PT64_INDEX(addr, level)
        #define PT_LEVEL_BITS PT64_LEVEL_BITS
        #ifdef CONFIG_X86_64
        #define PT_MAX_FULL_LEVELS 4
        #define CMPXCHG cmpxchg
        #else
        #define CMPXCHG cmpxchg64
        #define PT_MAX_FULL_LEVELS 2
        #endif
#elif PTTYPE == 32
        #define pt_element_t u32
        #define guest_walker guest_walker32
        #define FNAME(name) paging##32_##name
        #define PT_BASE_ADDR_MASK PT32_BASE_ADDR_MASK
        #define PT_LVL_ADDR_MASK(lvl) PT32_LVL_ADDR_MASK(lvl)
        #define PT_LVL_OFFSET_MASK(lvl) PT32_LVL_OFFSET_MASK(lvl)
        #define PT_INDEX(addr, level) PT32_INDEX(addr, level)
        #define PT_LEVEL_BITS PT32_LEVEL_BITS
        #define PT_MAX_FULL_LEVELS 2
        #define CMPXCHG cmpxchg
#else
        #error Invalid PTTYPE value
#endif

#define gpte_to_gfn_lvl FNAME(gpte_to_gfn_lvl)
#define gpte_to_gfn(pte) gpte_to_gfn_lvl((pte), PT_PAGE_TABLE_LEVEL)

/*
 * The guest_walker structure emulates the behavior of the hardware page
 * table walker.
 */
struct guest_walker {
        int level;
        unsigned max_level;
        gfn_t table_gfn[PT_MAX_FULL_LEVELS];
        pt_element_t ptes[PT_MAX_FULL_LEVELS];
        pt_element_t prefetch_ptes[PTE_PREFETCH_NUM];
        gpa_t pte_gpa[PT_MAX_FULL_LEVELS];
        pt_element_t __user *ptep_user[PT_MAX_FULL_LEVELS];
        unsigned pt_access;
        unsigned pte_access;
        gfn_t gfn;
        struct x86_exception fault;
};

static gfn_t gpte_to_gfn_lvl(pt_element_t gpte, int lvl)
{
        return (gpte & PT_LVL_ADDR_MASK(lvl)) >> PAGE_SHIFT;
}

static int FNAME(cmpxchg_gpte)(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
                               pt_element_t __user *ptep_user, unsigned index,
                               pt_element_t orig_pte, pt_element_t new_pte)
{
        int npages;
        pt_element_t ret;
        pt_element_t *table;
        struct page *page;

        npages = get_user_pages_fast((unsigned long)ptep_user, 1, 1, &page);
        /* Check if the user is doing something meaningless. */
        if (unlikely(npages != 1))
                return -EFAULT;

        table = kmap_atomic(page);
        ret = CMPXCHG(&table[index], orig_pte, new_pte);
        kunmap_atomic(table);

        kvm_release_page_dirty(page);

        return (ret != orig_pte);
}

static int FNAME(update_accessed_dirty_bits)(struct kvm_vcpu *vcpu,
                                             struct kvm_mmu *mmu,
                                             struct guest_walker *walker,
                                             int write_fault)
{
        unsigned level, index;
        pt_element_t pte, orig_pte;
        pt_element_t __user *ptep_user;
        gfn_t table_gfn;
        int ret;

        for (level = walker->max_level; level >= walker->level; --level) {
                pte = orig_pte = walker->ptes[level - 1];
                table_gfn = walker->table_gfn[level - 1];
                ptep_user = walker->ptep_user[level - 1];
                index = offset_in_page(ptep_user) / sizeof(pt_element_t);
                if (!(pte & PT_ACCESSED_MASK)) {
                        trace_kvm_mmu_set_accessed_bit(table_gfn, index, sizeof(pte));
                        pte |= PT_ACCESSED_MASK;
                }
                if (level == walker->level && write_fault && !is_dirty_gpte(pte)) {
                        trace_kvm_mmu_set_dirty_bit(table_gfn, index, sizeof(pte));
                        pte |= PT_DIRTY_MASK;
                }
                if (pte == orig_pte)
                        continue;

                ret = FNAME(cmpxchg_gpte)(vcpu, mmu, ptep_user, index, orig_pte, pte);
                if (ret)
                        return ret;

                mark_page_dirty(vcpu->kvm, table_gfn);
                walker->ptes[level] = pte;
        }
        return 0;
}

/*
 * Fetch a guest pte for a guest virtual address
 */
static int FNAME(walk_addr_generic)(struct guest_walker *walker,
                                    struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
                                    gva_t addr, u32 access)
{
        int ret;
        pt_element_t pte;
        pt_element_t __user *uninitialized_var(ptep_user);
        gfn_t table_gfn;
        unsigned index, pt_access, pte_access, accessed_dirty;
        gpa_t pte_gpa;
        int offset;
        const int write_fault = access & PFERR_WRITE_MASK;
        const int user_fault  = access & PFERR_USER_MASK;
        const int fetch_fault = access & PFERR_FETCH_MASK;
        u16 errcode = 0;
        gpa_t real_gpa;
        gfn_t gfn;

        trace_kvm_mmu_pagetable_walk(addr, access);
retry_walk:
        walker->level = mmu->root_level;
        pte           = mmu->get_cr3(vcpu);

#if PTTYPE == 64
        if (walker->level == PT32E_ROOT_LEVEL) {
                pte = mmu->get_pdptr(vcpu, (addr >> 30) & 3);
                trace_kvm_mmu_paging_element(pte, walker->level);
                if (!is_present_gpte(pte))
                        goto error;
                --walker->level;
        }
#endif
        walker->max_level = walker->level;
        ASSERT((!is_long_mode(vcpu) && is_pae(vcpu)) ||
               (mmu->get_cr3(vcpu) & CR3_NONPAE_RESERVED_BITS) == 0);

        accessed_dirty = PT_ACCESSED_MASK;
        pt_access = pte_access = ACC_ALL;
        ++walker->level;

        do {
                gfn_t real_gfn;
                unsigned long host_addr;

                pt_access &= pte_access;
                --walker->level;

                index = PT_INDEX(addr, walker->level);

                table_gfn = gpte_to_gfn(pte);
                offset    = index * sizeof(pt_element_t);
                pte_gpa   = gfn_to_gpa(table_gfn) + offset;
                walker->table_gfn[walker->level - 1] = table_gfn;
                walker->pte_gpa[walker->level - 1] = pte_gpa;

                real_gfn = mmu->translate_gpa(vcpu, gfn_to_gpa(table_gfn),
                                              PFERR_USER_MASK|PFERR_WRITE_MASK);
                if (unlikely(real_gfn == UNMAPPED_GVA))
                        goto error;
                real_gfn = gpa_to_gfn(real_gfn);

                host_addr = gfn_to_hva(vcpu->kvm, real_gfn);
                if (unlikely(kvm_is_error_hva(host_addr)))
                        goto error;

                ptep_user = (pt_element_t __user *)((void *)host_addr + offset);
                if (unlikely(__copy_from_user(&pte, ptep_user, sizeof(pte))))
                        goto error;
                walker->ptep_user[walker->level - 1] = ptep_user;

                trace_kvm_mmu_paging_element(pte, walker->level);

                if (unlikely(!is_present_gpte(pte)))
                        goto error;

                if (unlikely(is_rsvd_bits_set(&vcpu->arch.mmu, pte,
                                              walker->level))) {
                        errcode |= PFERR_RSVD_MASK | PFERR_PRESENT_MASK;
                        goto error;
                }

                accessed_dirty &= pte;
                pte_access = pt_access & gpte_access(vcpu, pte);

                walker->ptes[walker->level - 1] = pte;
        } while (!is_last_gpte(mmu, walker->level, pte));

        if (unlikely(permission_fault(mmu, pte_access, access))) {
                errcode |= PFERR_PRESENT_MASK;
                goto error;
        }

        gfn = gpte_to_gfn_lvl(pte, walker->level);
        gfn += (addr & PT_LVL_OFFSET_MASK(walker->level)) >> PAGE_SHIFT;

        if (PTTYPE == 32 && walker->level == PT_DIRECTORY_LEVEL && is_cpuid_PSE36())
                gfn += pse36_gfn_delta(pte);

        real_gpa = mmu->translate_gpa(vcpu, gfn_to_gpa(gfn), access);
        if (real_gpa == UNMAPPED_GVA)
                return 0;

        walker->gfn = real_gpa >> PAGE_SHIFT;

        if (!write_fault)
                protect_clean_gpte(&pte_access, pte);
        else
                /*
                 * On a write fault, fold the dirty bit into accessed_dirty by
                 * shifting it one place right.
                 */
                accessed_dirty &= pte >> (PT_DIRTY_SHIFT - PT_ACCESSED_SHIFT);

        if (unlikely(!accessed_dirty)) {
                ret = FNAME(update_accessed_dirty_bits)(vcpu, mmu, walker, write_fault);
                if (unlikely(ret < 0))
                        goto error;
                else if (ret)
                        goto retry_walk;
        }

        walker->pt_access = pt_access;
        walker->pte_access = pte_access;
        pgprintk("%s: pte %llx pte_access %x pt_access %x\n",
                 __func__, (u64)pte, pte_access, pt_access);
        return 1;

error:
        errcode |= write_fault | user_fault;
        if (fetch_fault && (mmu->nx ||
                            kvm_read_cr4_bits(vcpu, X86_CR4_SMEP)))
                errcode |= PFERR_FETCH_MASK;

        walker->fault.vector = PF_VECTOR;
        walker->fault.error_code_valid = true;
        walker->fault.error_code = errcode;
        walker->fault.address = addr;
        walker->fault.nested_page_fault = mmu != vcpu->arch.walk_mmu;

        trace_kvm_mmu_walker_error(walker->fault.error_code);
        return 0;
}

static int FNAME(walk_addr)(struct guest_walker *walker,
                            struct kvm_vcpu *vcpu, gva_t addr, u32 access)
{
        return FNAME(walk_addr_generic)(walker, vcpu, &vcpu->arch.mmu, addr,
                                        access);
}

static int FNAME(walk_addr_nested)(struct guest_walker *walker,
                                   struct kvm_vcpu *vcpu, gva_t addr,
                                   u32 access)
{
        return FNAME(walk_addr_generic)(walker, vcpu, &vcpu->arch.nested_mmu,
                                        addr, access);
}

static bool
FNAME(prefetch_gpte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
                     u64 *spte, pt_element_t gpte, bool no_dirty_log)
{
        unsigned pte_access;
        gfn_t gfn;
        pfn_t pfn;

        if (prefetch_invalid_gpte(vcpu, sp, spte, gpte))
                return false;

        pgprintk("%s: gpte %llx spte %p\n", __func__, (u64)gpte, spte);

        gfn = gpte_to_gfn(gpte);
        pte_access = sp->role.access & gpte_access(vcpu, gpte);
        protect_clean_gpte(&pte_access, gpte);
        pfn = pte_prefetch_gfn_to_pfn(vcpu, gfn,
                        no_dirty_log && (pte_access & ACC_WRITE_MASK));
        if (is_error_pfn(pfn))
                return false;

        /*
         * we call mmu_set_spte() with host_writable = true because
         * pte_prefetch_gfn_to_pfn always gets a writable pfn.
         */
        mmu_set_spte(vcpu, spte, sp->role.access, pte_access, 0, 0,
                     NULL, PT_PAGE_TABLE_LEVEL, gfn, pfn, true, true);

        return true;
}

static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
                              u64 *spte, const void *pte)
{
        pt_element_t gpte = *(const pt_element_t *)pte;

        FNAME(prefetch_gpte)(vcpu, sp, spte, gpte, false);
}

static bool FNAME(gpte_changed)(struct kvm_vcpu *vcpu,
                                struct guest_walker *gw, int level)
{
        pt_element_t curr_pte;
        gpa_t base_gpa, pte_gpa = gw->pte_gpa[level - 1];
        u64 mask;
        int r, index;

        if (level == PT_PAGE_TABLE_LEVEL) {
                mask = PTE_PREFETCH_NUM * sizeof(pt_element_t) - 1;
                base_gpa = pte_gpa & ~mask;
                index = (pte_gpa - base_gpa) / sizeof(pt_element_t);

                r = kvm_read_guest_atomic(vcpu->kvm, base_gpa,
                                gw->prefetch_ptes, sizeof(gw->prefetch_ptes));
                curr_pte = gw->prefetch_ptes[index];
        } else
                r = kvm_read_guest_atomic(vcpu->kvm, pte_gpa,
                                  &curr_pte, sizeof(curr_pte));

        return r || curr_pte != gw->ptes[level - 1];
}

static void FNAME(pte_prefetch)(struct kvm_vcpu *vcpu, struct guest_walker *gw,
                                u64 *sptep)
{
        struct kvm_mmu_page *sp;
        pt_element_t *gptep = gw->prefetch_ptes;
        u64 *spte;
        int i;

        sp = page_header(__pa(sptep));

        if (sp->role.level > PT_PAGE_TABLE_LEVEL)
                return;

        if (sp->role.direct)
                return __direct_pte_prefetch(vcpu, sp, sptep);

        i = (sptep - sp->spt) & ~(PTE_PREFETCH_NUM - 1);
        spte = sp->spt + i;

        for (i = 0; i < PTE_PREFETCH_NUM; i++, spte++) {
                if (spte == sptep)
                        continue;

                if (is_shadow_present_pte(*spte))
                        continue;

                if (!FNAME(prefetch_gpte)(vcpu, sp, spte, gptep[i], true))
                        break;
        }
}

/*
 * Fetch a shadow pte for a specific level in the paging hierarchy.
 * If the guest tries to write a write-protected page, we need to
 * emulate this operation, return 1 to indicate this case.
 */
static int FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
                         struct guest_walker *gw,
                         int user_fault, int write_fault, int hlevel,
                         pfn_t pfn, bool map_writable, bool prefault)
{
        struct kvm_mmu_page *sp = NULL;
        struct kvm_shadow_walk_iterator it;
        unsigned direct_access, access = gw->pt_access;
        int top_level, emulate = 0;

        if (!is_present_gpte(gw->ptes[gw->level - 1]))
                return 0;

        direct_access = gw->pte_access;

        top_level = vcpu->arch.mmu.root_level;
        if (top_level == PT32E_ROOT_LEVEL)
                top_level = PT32_ROOT_LEVEL;
        /*
         * Verify that the top-level gpte is still there.  Since the page
         * is a root page, it is either write protected (and cannot be
         * changed from now on) or it is invalid (in which case, we don't
         * really care if it changes underneath us after this point).
         */
        if (FNAME(gpte_changed)(vcpu, gw, top_level))
                goto out_gpte_changed;

        for (shadow_walk_init(&it, vcpu, addr);
             shadow_walk_okay(&it) && it.level > gw->level;
             shadow_walk_next(&it)) {
                gfn_t table_gfn;

                clear_sp_write_flooding_count(it.sptep);
                drop_large_spte(vcpu, it.sptep);

                sp = NULL;
                if (!is_shadow_present_pte(*it.sptep)) {
                        table_gfn = gw->table_gfn[it.level - 2];
                        sp = kvm_mmu_get_page(vcpu, table_gfn, addr, it.level-1,
                                              false, access, it.sptep);
                }

                /*
                 * Verify that the gpte in the page we've just write
                 * protected is still there.
                 */
                if (FNAME(gpte_changed)(vcpu, gw, it.level - 1))
                        goto out_gpte_changed;

                if (sp)
                        link_shadow_page(it.sptep, sp);
        }

        for (;
             shadow_walk_okay(&it) && it.level > hlevel;
             shadow_walk_next(&it)) {
                gfn_t direct_gfn;

                clear_sp_write_flooding_count(it.sptep);
                validate_direct_spte(vcpu, it.sptep, direct_access);

                drop_large_spte(vcpu, it.sptep);

                if (is_shadow_present_pte(*it.sptep))
                        continue;

                direct_gfn = gw->gfn & ~(KVM_PAGES_PER_HPAGE(it.level) - 1);

                sp = kvm_mmu_get_page(vcpu, direct_gfn, addr, it.level-1,
                                      true, direct_access, it.sptep);
                link_shadow_page(it.sptep, sp);
        }

        clear_sp_write_flooding_count(it.sptep);
        mmu_set_spte(vcpu, it.sptep, access, gw->pte_access,
                     user_fault, write_fault, &emulate, it.level,
                     gw->gfn, pfn, prefault, map_writable);
        FNAME(pte_prefetch)(vcpu, gw, it.sptep);

        return emulate;

out_gpte_changed:
        if (sp)
                kvm_mmu_put_page(sp, it.sptep);
        kvm_release_pfn_clean(pfn);
        return 0;
}

/*
 * Page fault handler.  There are several causes for a page fault:
 *   - there is no shadow pte for the guest pte
 *   - write access through a shadow pte marked read only so that we can set
 *     the dirty bit
 *   - write access to a shadow pte marked read only so we can update the page
 *     dirty bitmap, when userspace requests it
 *   - mmio access; in this case we will never install a present shadow pte
 *   - normal guest page fault due to the guest pte marked not present, not
 *     writable, or not executable
 *
 *  Returns: 1 if we need to emulate the instruction, 0 otherwise, or
 *           a negative value on error.
 */
static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,
                             bool prefault)
{
        int write_fault = error_code & PFERR_WRITE_MASK;
        int user_fault = error_code & PFERR_USER_MASK;
        struct guest_walker walker;
        int r;
        pfn_t pfn;
        int level = PT_PAGE_TABLE_LEVEL;
        int force_pt_level;
        unsigned long mmu_seq;
        bool map_writable;

        pgprintk("%s: addr %lx err %x\n", __func__, addr, error_code);

        if (unlikely(error_code & PFERR_RSVD_MASK))
                return handle_mmio_page_fault(vcpu, addr, error_code,
                                              mmu_is_nested(vcpu));

        r = mmu_topup_memory_caches(vcpu);
        if (r)
                return r;

        /*
         * Look up the guest pte for the faulting address.
         */
        r = FNAME(walk_addr)(&walker, vcpu, addr, error_code);

        /*
         * The page is not mapped by the guest.  Let the guest handle it.
         */
        if (!r) {
                pgprintk("%s: guest page fault\n", __func__);
                if (!prefault)
                        inject_page_fault(vcpu, &walker.fault);

                return 0;
        }

        if (walker.level >= PT_DIRECTORY_LEVEL)
                force_pt_level = mapping_level_dirty_bitmap(vcpu, walker.gfn);
        else
                force_pt_level = 1;
        if (!force_pt_level) {
                level = min(walker.level, mapping_level(vcpu, walker.gfn));
                walker.gfn = walker.gfn & ~(KVM_PAGES_PER_HPAGE(level) - 1);
        }

        mmu_seq = vcpu->kvm->mmu_notifier_seq;
        smp_rmb();

        if (try_async_pf(vcpu, prefault, walker.gfn, addr, &pfn, write_fault,
                         &map_writable))
                return 0;

        if (handle_abnormal_pfn(vcpu, mmu_is_nested(vcpu) ? 0 : addr,
                                walker.gfn, pfn, walker.pte_access, &r))
                return r;

        spin_lock(&vcpu->kvm->mmu_lock);
        if (mmu_notifier_retry(vcpu->kvm, mmu_seq))
                goto out_unlock;

        kvm_mmu_audit(vcpu, AUDIT_PRE_PAGE_FAULT);
        kvm_mmu_free_some_pages(vcpu);
        if (!force_pt_level)
                transparent_hugepage_adjust(vcpu, &walker.gfn, &pfn, &level);
        r = FNAME(fetch)(vcpu, addr, &walker, user_fault, write_fault,
                         level, pfn, map_writable, prefault);
        ++vcpu->stat.pf_fixed;
        kvm_mmu_audit(vcpu, AUDIT_POST_PAGE_FAULT);
        spin_unlock(&vcpu->kvm->mmu_lock);

        return r;

out_unlock:
        spin_unlock(&vcpu->kvm->mmu_lock);
        kvm_release_pfn_clean(pfn);
        return 0;
}

static gpa_t FNAME(get_level1_sp_gpa)(struct kvm_mmu_page *sp)
{
        int offset = 0;

        WARN_ON(sp->role.level != PT_PAGE_TABLE_LEVEL);

        if (PTTYPE == 32)
                offset = sp->role.quadrant << PT64_LEVEL_BITS;

        return gfn_to_gpa(sp->gfn) + offset * sizeof(pt_element_t);
}

static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva)
{
        struct kvm_shadow_walk_iterator iterator;
        struct kvm_mmu_page *sp;
        int level;
        u64 *sptep;

        vcpu_clear_mmio_info(vcpu, gva);

        /*
         * No need to check return value here, rmap_can_add() can
         * help us to skip pte prefetch later.
         */
        mmu_topup_memory_caches(vcpu);

        spin_lock(&vcpu->kvm->mmu_lock);
        for_each_shadow_entry(vcpu, gva, iterator) {
                level = iterator.level;
                sptep = iterator.sptep;

                sp = page_header(__pa(sptep));
                if (is_last_spte(*sptep, level)) {
                        pt_element_t gpte;
                        gpa_t pte_gpa;

                        if (!sp->unsync)
                                break;

                        pte_gpa = FNAME(get_level1_sp_gpa)(sp);
                        pte_gpa += (sptep - sp->spt) * sizeof(pt_element_t);

                        if (mmu_page_zap_pte(vcpu->kvm, sp, sptep))
                                kvm_flush_remote_tlbs(vcpu->kvm);

                        if (!rmap_can_add(vcpu))
                                break;

                        if (kvm_read_guest_atomic(vcpu->kvm, pte_gpa, &gpte,
                                                  sizeof(pt_element_t)))
                                break;

                        FNAME(update_pte)(vcpu, sp, sptep, &gpte);
                }

                if (!is_shadow_present_pte(*sptep) || !sp->unsync_children)
                        break;
        }
        spin_unlock(&vcpu->kvm->mmu_lock);
}

static gpa_t FNAME(gva_to_gpa)(struct kvm_vcpu *vcpu, gva_t vaddr, u32 access,
                               struct x86_exception *exception)
{
        struct guest_walker walker;
        gpa_t gpa = UNMAPPED_GVA;
        int r;

        r = FNAME(walk_addr)(&walker, vcpu, vaddr, access);

        if (r) {
                gpa = gfn_to_gpa(walker.gfn);
                gpa |= vaddr & ~PAGE_MASK;
        } else if (exception)
                *exception = walker.fault;

        return gpa;
}

static gpa_t FNAME(gva_to_gpa_nested)(struct kvm_vcpu *vcpu, gva_t vaddr,
                                      u32 access,
                                      struct x86_exception *exception)
{
        struct guest_walker walker;
        gpa_t gpa = UNMAPPED_GVA;
        int r;

        r = FNAME(walk_addr_nested)(&walker, vcpu, vaddr, access);

        if (r) {
                gpa = gfn_to_gpa(walker.gfn);
                gpa |= vaddr & ~PAGE_MASK;
        } else if (exception)
                *exception = walker.fault;

        return gpa;
}

/*
 * Using the cached information from sp->gfns is safe because:
 * - The spte has a reference to the struct page, so the pfn for a given gfn
 *   can't change unless all sptes pointing to it are nuked first.
 *
 * Note:
 *   We should flush all tlbs if spte is dropped even though guest is
 *   responsible for it. Since if we don't, kvm_mmu_notifier_invalidate_page
 *   and kvm_mmu_notifier_invalidate_range_start detect the mapping page isn't
 *   used by guest then tlbs are not flushed, so guest is allowed to access the
 *   freed pages.
 *   And we increase kvm->tlbs_dirty to delay tlbs flush in this case.
 */
static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
{
        int i, nr_present = 0;
        bool host_writable;
        gpa_t first_pte_gpa;

        /* direct kvm_mmu_page can not be unsync. */
        BUG_ON(sp->role.direct);

        first_pte_gpa = FNAME(get_level1_sp_gpa)(sp);

        for (i = 0; i < PT64_ENT_PER_PAGE; i++) {
                unsigned pte_access;
                pt_element_t gpte;
                gpa_t pte_gpa;
                gfn_t gfn;

                if (!sp->spt[i])
                        continue;

                pte_gpa = first_pte_gpa + i * sizeof(pt_element_t);

                if (kvm_read_guest_atomic(vcpu->kvm, pte_gpa, &gpte,
                                          sizeof(pt_element_t)))
                        return -EINVAL;

                if (prefetch_invalid_gpte(vcpu, sp, &sp->spt[i], gpte)) {
                        vcpu->kvm->tlbs_dirty++;
                        continue;
                }

                gfn = gpte_to_gfn(gpte);
                pte_access = sp->role.access;
                pte_access &= gpte_access(vcpu, gpte);
                protect_clean_gpte(&pte_access, gpte);

                if (sync_mmio_spte(&sp->spt[i], gfn, pte_access, &nr_present))
                        continue;

                if (gfn != sp->gfns[i]) {
                        drop_spte(vcpu->kvm, &sp->spt[i]);
                        vcpu->kvm->tlbs_dirty++;
                        continue;
                }

                nr_present++;

                host_writable = sp->spt[i] & SPTE_HOST_WRITEABLE;

                set_spte(vcpu, &sp->spt[i], pte_access, 0, 0,
                         PT_PAGE_TABLE_LEVEL, gfn,
                         spte_to_pfn(sp->spt[i]), true, false,
                         host_writable);
        }

        return !nr_present;
}

#undef pt_element_t
#undef guest_walker
#undef FNAME
#undef PT_BASE_ADDR_MASK
#undef PT_INDEX
#undef PT_LVL_ADDR_MASK
#undef PT_LVL_OFFSET_MASK
#undef PT_LEVEL_BITS
#undef PT_MAX_FULL_LEVELS
#undef gpte_to_gfn
#undef gpte_to_gfn_lvl
#undef CMPXCHG