Commit message: X86/KVM: Handle PFNs outside of kernel reach when touching GPTEs

cmpxchg_gpte() calls get_user_pages_fast() to retrieve the number of
pages and the respective struct page to map in the kernel virtual
address space.
This doesn't work if get_user_pages_fast() is invoked with a userspace
virtual address that's backed by PFNs outside of kernel reach (e.g., when
limiting the kernel memory with mem= in the command line and using
/dev/mem to map memory).

If get_user_pages_fast() fails, look up the VMA that back the userspace
virtual address, compute the PFN and the physical address, and map it in
the kernel virtual address space with memremap().

Signed-off-by: Filippo Sironi <sironi@amazon.de>
Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
CVE: CVE-2022-1158
Vulnerability description: A flaw was found in KVM. When updating a guest's page table entry, vm_pgoff was improperly used as the offset to get the page's pfn. As vaddr and vm_pgoff are controllable by user-mode processes, this flaw allows unprivileged local users on the host to write outside the userspace region and potentially corrupt the kernel, resulting in a denial of service condition.

Project: linux

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);
}

Project: linux

FNAME(is_self_change_mapping)(struct kvm_vcpu *vcpu,
			      struct guest_walker *walker, int user_fault,
			      bool *write_fault_to_shadow_pgtable)
{
	int level;
	gfn_t mask = ~(KVM_PAGES_PER_HPAGE(walker->level) - 1);
	bool self_changed = false;

	if (!(walker->pte_access & ACC_WRITE_MASK ||
	      (!is_write_protection(vcpu) && !user_fault)))
		return false;

	for (level = walker->level; level <= walker->max_level; level++) {
		gfn_t gfn = walker->gfn ^ walker->table_gfn[level - 1];

		self_changed |= !(gfn & mask);
		*write_fault_to_shadow_pgtable |= !gfn;
	}

	return self_changed;
}

Project: linux

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;
	kvm_pfn_t pfn;

	if (FNAME(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 & FNAME(gpte_access)(gpte);
	FNAME(protect_clean_gpte)(vcpu->arch.mmu, &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, pte_access, 0, PT_PAGE_TABLE_LEVEL, gfn, pfn,
		     true, true);

	return true;
}

Project: linux
File: paging_tmpl.h

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;
}

Project: linux

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;
	}
}

Project: linux
File: paging_tmpl.h

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;
}

Project: linux

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);
	if (likely(npages == 1)) {
		table = kmap_atomic(page);
		ret = CMPXCHG(&table[index], orig_pte, new_pte);
		kunmap_atomic(table);

		kvm_release_page_dirty(page);
	} else {
		struct vm_area_struct *vma;
		unsigned long vaddr = (unsigned long)ptep_user & PAGE_MASK;
		unsigned long pfn;
		unsigned long paddr;

		down_read(&current->mm->mmap_sem);
		vma = find_vma_intersection(current->mm, vaddr, vaddr + PAGE_SIZE);
		if (!vma || !(vma->vm_flags & VM_PFNMAP)) {
			up_read(&current->mm->mmap_sem);
			return -EFAULT;
		}
		pfn = ((vaddr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
		paddr = pfn << PAGE_SHIFT;
		table = memremap(paddr, PAGE_SIZE, MEMREMAP_WB);
		if (!table) {
			up_read(&current->mm->mmap_sem);
			return -EFAULT;
		}
		ret = CMPXCHG(&table[index], orig_pte, new_pte);
		memunmap(table);
		up_read(&current->mm->mmap_sem);
	}

	return (ret != orig_pte);
}

Project: linux

static bool FNAME(prefetch_invalid_gpte)(struct kvm_vcpu *vcpu,
				  struct kvm_mmu_page *sp, u64 *spte,
				  u64 gpte)
{
	if (is_rsvd_bits_set(vcpu->arch.mmu, gpte, PT_PAGE_TABLE_LEVEL))
		goto no_present;

	if (!FNAME(is_present_gpte)(gpte))
		goto no_present;

	/* if accessed bit is not supported prefetch non accessed gpte */
	if (PT_HAVE_ACCESSED_DIRTY(vcpu->arch.mmu) &&
	    !(gpte & PT_GUEST_ACCESSED_MASK))
		goto no_present;

	return false;

no_present:
	drop_spte(vcpu->kvm, spte);
	return true;
}

Project: linux

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

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

Project: linux

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;
	int set_spte_ret = 0;

	/* 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_vcpu_read_guest_atomic(vcpu, pte_gpa, &gpte,
					       sizeof(pt_element_t)))
			return 0;

		if (FNAME(prefetch_invalid_gpte)(vcpu, sp, &sp->spt[i], gpte)) {
			/*
			 * Update spte before increasing tlbs_dirty to make
			 * sure no tlb flush is lost after spte is zapped; see
			 * the comments in kvm_flush_remote_tlbs().
			 */
			smp_wmb();
			vcpu->kvm->tlbs_dirty++;
			continue;
		}

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

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

		if (gfn != sp->gfns[i]) {
			drop_spte(vcpu->kvm, &sp->spt[i]);
			/*
			 * The same as above where we are doing
			 * prefetch_invalid_gpte().
			 */
			smp_wmb();
			vcpu->kvm->tlbs_dirty++;
			continue;
		}

		nr_present++;

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

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

	if (set_spte_ret & SET_SPTE_NEED_REMOTE_TLB_FLUSH)
		kvm_flush_remote_tlbs(vcpu->kvm);

	return nr_present;
}

Project: linux

static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva, hpa_t root_hpa)
{
	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);

	if (!VALID_PAGE(root_hpa)) {
		WARN_ON(1);
		return;
	}

	spin_lock(&vcpu->kvm->mmu_lock);
	for_each_shadow_entry_using_root(vcpu, root_hpa, 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_with_address(vcpu->kvm,
					sp->gfn, KVM_PAGES_PER_HPAGE(sp->role.level));

			if (!rmap_can_add(vcpu))
				break;

			if (kvm_vcpu_read_guest_atomic(vcpu, 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);
}

Project: linux

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);
}

Project: linux

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;
	u64 pt_access, pte_access;
	unsigned index, accessed_dirty, pte_pkey;
	unsigned nested_access;
	gpa_t pte_gpa;
	bool have_ad;
	int offset;
	u64 walk_nx_mask = 0;
	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);
	have_ad       = PT_HAVE_ACCESSED_DIRTY(mmu);

#if PTTYPE == 64
	walk_nx_mask = 1ULL << PT64_NX_SHIFT;
	if (walker->level == PT32E_ROOT_LEVEL) {
		pte = mmu->get_pdptr(vcpu, (addr >> 30) & 3);
		trace_kvm_mmu_paging_element(pte, walker->level);
		if (!FNAME(is_present_gpte)(pte))
			goto error;
		--walker->level;
	}
#endif
	walker->max_level = walker->level;
	ASSERT(!(is_long_mode(vcpu) && !is_pae(vcpu)));

	/*
	 * FIXME: on Intel processors, loads of the PDPTE registers for PAE paging
	 * by the MOV to CR instruction are treated as reads and do not cause the
	 * processor to set the dirty flag in any EPT paging-structure entry.
	 */
	nested_access = (have_ad ? PFERR_WRITE_MASK : 0) | PFERR_USER_MASK;

	pte_access = ~0;
	++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;

		BUG_ON(walker->level < 1);
		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),
					      nested_access,
					      &walker->fault);

		/*
		 * FIXME: This can happen if emulation (for of an INS/OUTS
		 * instruction) triggers a nested page fault.  The exit
		 * qualification / exit info field will incorrectly have
		 * "guest page access" as the nested page fault's cause,
		 * instead of "guest page structure access".  To fix this,
		 * the x86_exception struct should be augmented with enough
		 * information to fix the exit_qualification or exit_info_1
		 * fields.
		 */
		if (unlikely(real_gfn == UNMAPPED_GVA))
			return 0;

		real_gfn = gpa_to_gfn(real_gfn);

		host_addr = kvm_vcpu_gfn_to_hva_prot(vcpu, real_gfn,
					    &walker->pte_writable[walker->level - 1]);
		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);

		/*
		 * Inverting the NX it lets us AND it like other
		 * permission bits.
		 */
		pte_access = pt_access & (pte ^ walk_nx_mask);

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

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

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

	pte_pkey = FNAME(gpte_pkeys)(vcpu, pte);
	accessed_dirty = have_ad ? pte_access & PT_GUEST_ACCESSED_MASK : 0;

	/* Convert to ACC_*_MASK flags for struct guest_walker.  */
	walker->pt_access = FNAME(gpte_access)(pt_access ^ walk_nx_mask);
	walker->pte_access = FNAME(gpte_access)(pte_access ^ walk_nx_mask);
	errcode = permission_fault(vcpu, mmu, walker->pte_access, pte_pkey, access);
	if (unlikely(errcode))
		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, &walker->fault);
	if (real_gpa == UNMAPPED_GVA)
		return 0;

	walker->gfn = real_gpa >> PAGE_SHIFT;

	if (!write_fault)
		FNAME(protect_clean_gpte)(mmu, &walker->pte_access, pte);
	else
		/*
		 * On a write fault, fold the dirty bit into accessed_dirty.
		 * For modes without A/D bits support accessed_dirty will be
		 * always clear.
		 */
		accessed_dirty &= pte >>
			(PT_GUEST_DIRTY_SHIFT - PT_GUEST_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;
	}

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

#if PTTYPE == PTTYPE_EPT
	/*
	 * Use PFERR_RSVD_MASK in error_code to to tell if EPT
	 * misconfiguration requires to be injected. The detection is
	 * done by is_rsvd_bits_set() above.
	 *
	 * We set up the value of exit_qualification to inject:
	 * [2:0] - Derive from the access bits. The exit_qualification might be
	 *         out of date if it is serving an EPT misconfiguration.
	 * [5:3] - Calculated by the page walk of the guest EPT page tables
	 * [7:8] - Derived from [7:8] of real exit_qualification
	 *
	 * The other bits are set to 0.
	 */
	if (!(errcode & PFERR_RSVD_MASK)) {
		vcpu->arch.exit_qualification &= 0x180;
		if (write_fault)
			vcpu->arch.exit_qualification |= EPT_VIOLATION_ACC_WRITE;
		if (user_fault)
			vcpu->arch.exit_qualification |= EPT_VIOLATION_ACC_READ;
		if (fetch_fault)
			vcpu->arch.exit_qualification |= EPT_VIOLATION_ACC_INSTR;
		vcpu->arch.exit_qualification |= (pte_access & 0x7) << 3;
	}
#endif
	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;
}

Project: linux

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;

	/* dirty/accessed bits are not supported, so no need to update them */
	if (!PT_HAVE_ACCESSED_DIRTY(mmu))
		return 0;

	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_GUEST_ACCESSED_MASK)) {
			trace_kvm_mmu_set_accessed_bit(table_gfn, index, sizeof(pte));
			pte |= PT_GUEST_ACCESSED_MASK;
		}
		if (level == walker->level && write_fault &&
				!(pte & PT_GUEST_DIRTY_MASK)) {
			trace_kvm_mmu_set_dirty_bit(table_gfn, index, sizeof(pte));
#if PTTYPE == PTTYPE_EPT
			if (kvm_arch_write_log_dirty(vcpu))
				return -EINVAL;
#endif
			pte |= PT_GUEST_DIRTY_MASK;
		}
		if (pte == orig_pte)
			continue;

		/*
		 * If the slot is read-only, simply do not process the accessed
		 * and dirty bits.  This is the correct thing to do if the slot
		 * is ROM, and page tables in read-as-ROM/write-as-MMIO slots
		 * are only supported if the accessed and dirty bits are already
		 * set in the ROM (so that MMIO writes are never needed).
		 *
		 * Note that NPT does not allow this at all and faults, since
		 * it always wants nested page table entries for the guest
		 * page tables to be writable.  And EPT works but will simply
		 * overwrite the read-only memory to set the accessed and dirty
		 * bits.
		 */
		if (unlikely(!walker->pte_writable[level - 1]))
			continue;

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

		kvm_vcpu_mark_page_dirty(vcpu, table_gfn);
		walker->ptes[level - 1] = pte;
	}
	return 0;
}

Project: linux

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;
	kvm_pfn_t pfn;
	int level = PT_PAGE_TABLE_LEVEL;
	bool force_pt_level = false;
	unsigned long mmu_seq;
	bool map_writable, is_self_change_mapping;

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

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

	/*
	 * If PFEC.RSVD is set, this is a shadow page fault.
	 * The bit needs to be cleared before walking guest page tables.
	 */
	error_code &= ~PFERR_RSVD_MASK;

	/*
	 * 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 RET_PF_RETRY;
	}

	if (page_fault_handle_page_track(vcpu, error_code, walker.gfn)) {
		shadow_page_table_clear_flood(vcpu, addr);
		return RET_PF_EMULATE;
	}

	vcpu->arch.write_fault_to_shadow_pgtable = false;

	is_self_change_mapping = FNAME(is_self_change_mapping)(vcpu,
	      &walker, user_fault, &vcpu->arch.write_fault_to_shadow_pgtable);

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

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

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

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

	/*
	 * Do not change pte_access if the pfn is a mmio page, otherwise
	 * we will cache the incorrect access into mmio spte.
	 */
	if (write_fault && !(walker.pte_access & ACC_WRITE_MASK) &&
	     !is_write_protection(vcpu) && !user_fault &&
	      !is_noslot_pfn(pfn)) {
		walker.pte_access |= ACC_WRITE_MASK;
		walker.pte_access &= ~ACC_USER_MASK;

		/*
		 * If we converted a user page to a kernel page,
		 * so that the kernel can write to it when cr0.wp=0,
		 * then we should prevent the kernel from executing it
		 * if SMEP is enabled.
		 */
		if (kvm_read_cr4_bits(vcpu, X86_CR4_SMEP))
			walker.pte_access &= ~ACC_EXEC_MASK;
	}

	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);
	if (make_mmu_pages_available(vcpu) < 0)
		goto out_unlock;
	if (!force_pt_level)
		transparent_hugepage_adjust(vcpu, &walker.gfn, &pfn, &level);
	r = FNAME(fetch)(vcpu, addr, &walker, 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 RET_PF_RETRY;
}

Project: linux

static int FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
			 struct guest_walker *gw,
			 int write_fault, int hlevel,
			 kvm_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, ret;

	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;

	if (!VALID_PAGE(vcpu->arch.mmu->root_hpa))
		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);
		}

		/*
		 * 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(vcpu, 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);
		link_shadow_page(vcpu, it.sptep, sp);
	}

	clear_sp_write_flooding_count(it.sptep);
	ret = mmu_set_spte(vcpu, it.sptep, gw->pte_access, write_fault,
			   it.level, gw->gfn, pfn, prefault, map_writable);
	FNAME(pte_prefetch)(vcpu, gw, it.sptep);

	return ret;

out_gpte_changed:
	kvm_release_pfn_clean(pfn);
	return RET_PF_RETRY;
}