arch/x86/kvm/paging_tmpl.h - third_party/linux - Git at Google

 /*
  * 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.
  *
  * 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_DIR_BASE_ADDR_MASK PT64_DIR_BASE_ADDR_MASK
 	#define PT_INDEX(addr, level) PT64_INDEX(addr, level)
 	#define SHADOW_PT_INDEX(addr, level) PT64_INDEX(addr, level)
 	#define PT_LEVEL_MASK(level) PT64_LEVEL_MASK(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_DIR_BASE_ADDR_MASK PT32_DIR_BASE_ADDR_MASK
 	#define PT_INDEX(addr, level) PT32_INDEX(addr, level)
 	#define SHADOW_PT_INDEX(addr, level) PT64_INDEX(addr, level)
 	#define PT_LEVEL_MASK(level) PT32_LEVEL_MASK(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 FNAME(gpte_to_gfn)
 #define gpte_to_gfn_pde FNAME(gpte_to_gfn_pde)

 /*
  * The guest_walker structure emulates the behavior of the hardware page
  * table walker.
  */
 struct guest_walker {
 	int level;
 	gfn_t table_gfn[PT_MAX_FULL_LEVELS];
 	pt_element_t ptes[PT_MAX_FULL_LEVELS];
 	gpa_t pte_gpa[PT_MAX_FULL_LEVELS];
 	unsigned pt_access;
 	unsigned pte_access;
 	gfn_t gfn;
 	u32 error_code;
 };

 static gfn_t gpte_to_gfn(pt_element_t gpte)
 {
 	return (gpte & PT_BASE_ADDR_MASK) >> PAGE_SHIFT;
 }

 static gfn_t gpte_to_gfn_pde(pt_element_t gpte)
 {
 	return (gpte & PT_DIR_BASE_ADDR_MASK) >> PAGE_SHIFT;
 }

 static bool FNAME(cmpxchg_gpte)(struct kvm *kvm,
 			 gfn_t table_gfn, unsigned index,
 			 pt_element_t orig_pte, pt_element_t new_pte)
 {
 	pt_element_t ret;
 	pt_element_t *table;
 	struct page *page;

 	down_read(&current->mm->mmap_sem);
 	page = gfn_to_page(kvm, table_gfn);
 	up_read(&current->mm->mmap_sem);

 	table = kmap_atomic(page, KM_USER0);

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

 	kunmap_atomic(table, KM_USER0);

 	kvm_release_page_dirty(page);

 	return (ret != orig_pte);
 }

 static unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu, pt_element_t gpte)
 {
 	unsigned access;

 	access = (gpte & (PT_WRITABLE_MASK | PT_USER_MASK)) | ACC_EXEC_MASK;
 #if PTTYPE == 64
 	if (is_nx(vcpu))
 		access &= ~(gpte >> PT64_NX_SHIFT);
 #endif
 	return access;
 }

 /*
  * Fetch a guest pte for a guest virtual address
  */
 static int FNAME(walk_addr)(struct guest_walker *walker,
 			    struct kvm_vcpu *vcpu, gva_t addr,
 			    int write_fault, int user_fault, int fetch_fault)
 {
 	pt_element_t pte;
 	gfn_t table_gfn;
 	unsigned index, pt_access, pte_access;
 	gpa_t pte_gpa;

 	pgprintk("%s: addr %lx\n", __FUNCTION__, addr);
 walk:
 	walker->level = vcpu->arch.mmu.root_level;
 	pte = vcpu->arch.cr3;
 #if PTTYPE == 64
 	if (!is_long_mode(vcpu)) {
 		pte = vcpu->arch.pdptrs[(addr >> 30) & 3];
 		if (!is_present_pte(pte))
 			goto not_present;
 		--walker->level;
 	}
 #endif
 	ASSERT((!is_long_mode(vcpu) && is_pae(vcpu)) ||
 	       (vcpu->arch.cr3 & CR3_NONPAE_RESERVED_BITS) == 0);

 	pt_access = ACC_ALL;

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

 		table_gfn = gpte_to_gfn(pte);
 		pte_gpa = gfn_to_gpa(table_gfn);
 		pte_gpa += index * sizeof(pt_element_t);
 		walker->table_gfn[walker->level - 1] = table_gfn;
 		walker->pte_gpa[walker->level - 1] = pte_gpa;
 		pgprintk("%s: table_gfn[%d] %lx\n", __FUNCTION__,
 			 walker->level - 1, table_gfn);

 		kvm_read_guest(vcpu->kvm, pte_gpa, &pte, sizeof(pte));

 		if (!is_present_pte(pte))
 			goto not_present;

 		if (write_fault && !is_writeble_pte(pte))
 			if (user_fault || is_write_protection(vcpu))
 				goto access_error;

 		if (user_fault && !(pte & PT_USER_MASK))
 			goto access_error;

 #if PTTYPE == 64
 		if (fetch_fault && is_nx(vcpu) && (pte & PT64_NX_MASK))
 			goto access_error;
 #endif

 		if (!(pte & PT_ACCESSED_MASK)) {
 			mark_page_dirty(vcpu->kvm, table_gfn);
 			if (FNAME(cmpxchg_gpte)(vcpu->kvm, table_gfn,
 			    index, pte, pte|PT_ACCESSED_MASK))
 				goto walk;
 			pte |= PT_ACCESSED_MASK;
 		}

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

 		walker->ptes[walker->level - 1] = pte;

 		if (walker->level == PT_PAGE_TABLE_LEVEL) {
 			walker->gfn = gpte_to_gfn(pte);
 			break;
 		}

 		if (walker->level == PT_DIRECTORY_LEVEL
 		    && (pte & PT_PAGE_SIZE_MASK)
 		    && (PTTYPE == 64 || is_pse(vcpu))) {
 			walker->gfn = gpte_to_gfn_pde(pte);
 			walker->gfn += PT_INDEX(addr, PT_PAGE_TABLE_LEVEL);
 			if (PTTYPE == 32 && is_cpuid_PSE36())
 				walker->gfn += pse36_gfn_delta(pte);
 			break;
 		}

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

 	if (write_fault && !is_dirty_pte(pte)) {
 		bool ret;

 		mark_page_dirty(vcpu->kvm, table_gfn);
 		ret = FNAME(cmpxchg_gpte)(vcpu->kvm, table_gfn, index, pte,
 			    pte|PT_DIRTY_MASK);
 		if (ret)
 			goto walk;
 		pte |= PT_DIRTY_MASK;
 		kvm_mmu_pte_write(vcpu, pte_gpa, (u8 *)&pte, sizeof(pte));
 		walker->ptes[walker->level - 1] = pte;
 	}

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

 not_present:
 	walker->error_code = 0;
 	goto err;

 access_error:
 	walker->error_code = PFERR_PRESENT_MASK;

 err:
 	if (write_fault)
 		walker->error_code |= PFERR_WRITE_MASK;
 	if (user_fault)
 		walker->error_code |= PFERR_USER_MASK;
 	if (fetch_fault)
 		walker->error_code |= PFERR_FETCH_MASK;
 	return 0;
 }

 static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *page,
 			      u64 *spte, const void *pte, int bytes,
 			      int offset_in_pte)
 {
 	pt_element_t gpte;
 	unsigned pte_access;
 	struct page *npage;

 	gpte = *(const pt_element_t *)pte;
 	if (~gpte & (PT_PRESENT_MASK | PT_ACCESSED_MASK)) {
 		if (!offset_in_pte && !is_present_pte(gpte))
 			set_shadow_pte(spte, shadow_notrap_nonpresent_pte);
 		return;
 	}
 	if (bytes < sizeof(pt_element_t))
 		return;
 	pgprintk("%s: gpte %llx spte %p\n", __FUNCTION__, (u64)gpte, spte);
 	pte_access = page->role.access & FNAME(gpte_access)(vcpu, gpte);
 	if (gpte_to_gfn(gpte) != vcpu->arch.update_pte.gfn)
 		return;
 	npage = vcpu->arch.update_pte.page;
 	if (!npage)
 		return;
 	get_page(npage);
 	mmu_set_spte(vcpu, spte, page->role.access, pte_access, 0, 0,
 		     gpte & PT_DIRTY_MASK, NULL, gpte_to_gfn(gpte), npage);
 }

 /*
  * Fetch a shadow pte for a specific level in the paging hierarchy.
  */
 static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
 			 struct guest_walker *walker,
 			 int user_fault, int write_fault, int *ptwrite,
 			 struct page *page)
 {
 	hpa_t shadow_addr;
 	int level;
 	u64 *shadow_ent;
 	unsigned access = walker->pt_access;

 	if (!is_present_pte(walker->ptes[walker->level - 1]))
 		return NULL;

 	shadow_addr = vcpu->arch.mmu.root_hpa;
 	level = vcpu->arch.mmu.shadow_root_level;
 	if (level == PT32E_ROOT_LEVEL) {
 		shadow_addr = vcpu->arch.mmu.pae_root[(addr >> 30) & 3];
 		shadow_addr &= PT64_BASE_ADDR_MASK;
 		--level;
 	}

 	for (; ; level--) {
 		u32 index = SHADOW_PT_INDEX(addr, level);
 		struct kvm_mmu_page *shadow_page;
 		u64 shadow_pte;
 		int metaphysical;
 		gfn_t table_gfn;

 		shadow_ent = ((u64 *)__va(shadow_addr)) + index;
 		if (level == PT_PAGE_TABLE_LEVEL)
 			break;
 		if (is_shadow_present_pte(*shadow_ent)) {
 			shadow_addr = *shadow_ent & PT64_BASE_ADDR_MASK;
 			continue;
 		}

 		if (level - 1 == PT_PAGE_TABLE_LEVEL
 		    && walker->level == PT_DIRECTORY_LEVEL) {
 			metaphysical = 1;
 			if (!is_dirty_pte(walker->ptes[level - 1]))
 				access &= ~ACC_WRITE_MASK;
 			table_gfn = gpte_to_gfn(walker->ptes[level - 1]);
 		} else {
 			metaphysical = 0;
 			table_gfn = walker->table_gfn[level - 2];
 		}
 		shadow_page = kvm_mmu_get_page(vcpu, table_gfn, addr, level-1,
 					       metaphysical, access,
 					       shadow_ent);
 		if (!metaphysical) {
 			int r;
 			pt_element_t curr_pte;
 			r = kvm_read_guest_atomic(vcpu->kvm,
 						  walker->pte_gpa[level - 2],
 						  &curr_pte, sizeof(curr_pte));
 			if (r || curr_pte != walker->ptes[level - 2]) {
 				kvm_release_page_clean(page);
 				return NULL;
 			}
 		}
 		shadow_addr = __pa(shadow_page->spt);
 		shadow_pte = shadow_addr | PT_PRESENT_MASK | PT_ACCESSED_MASK
 			| PT_WRITABLE_MASK | PT_USER_MASK;
 		*shadow_ent = shadow_pte;
 	}

 	mmu_set_spte(vcpu, shadow_ent, access, walker->pte_access & access,
 		     user_fault, write_fault,
 		     walker->ptes[walker->level-1] & PT_DIRTY_MASK,
 		     ptwrite, walker->gfn, page);

 	return shadow_ent;
 }

 /*
  * 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)
 {
 	int write_fault = error_code & PFERR_WRITE_MASK;
 	int user_fault = error_code & PFERR_USER_MASK;
 	int fetch_fault = error_code & PFERR_FETCH_MASK;
 	struct guest_walker walker;
 	u64 *shadow_pte;
 	int write_pt = 0;
 	int r;
 	struct page *page;

 	pgprintk("%s: addr %lx err %x\n", __FUNCTION__, addr, error_code);
 	kvm_mmu_audit(vcpu, "pre page fault");

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

 	down_read(&vcpu->kvm->slots_lock);
 	/*
 	 * Look up the shadow pte for the faulting address.
 	 */
 	r = FNAME(walk_addr)(&walker, vcpu, addr, write_fault, user_fault,
 			     fetch_fault);

 	/*
 	 * The page is not mapped by the guest.  Let the guest handle it.
 	 */
 	if (!r) {
 		pgprintk("%s: guest page fault\n", __FUNCTION__);
 		inject_page_fault(vcpu, addr, walker.error_code);
 		vcpu->arch.last_pt_write_count = 0; /* reset fork detector */
 		up_read(&vcpu->kvm->slots_lock);
 		return 0;
 	}

 	down_read(&current->mm->mmap_sem);
 	page = gfn_to_page(vcpu->kvm, walker.gfn);
 	up_read(&current->mm->mmap_sem);

 	spin_lock(&vcpu->kvm->mmu_lock);
 	kvm_mmu_free_some_pages(vcpu);
 	shadow_pte = FNAME(fetch)(vcpu, addr, &walker, user_fault, write_fault,
 				  &write_pt, page);
 	pgprintk("%s: shadow pte %p %llx ptwrite %d\n", __FUNCTION__,
 		 shadow_pte, *shadow_pte, write_pt);

 	if (!write_pt)
 		vcpu->arch.last_pt_write_count = 0; /* reset fork detector */

 	/*
 	 * mmio: emulate if accessible, otherwise its a guest fault.
 	 */
 	if (shadow_pte && is_io_pte(*shadow_pte)) {
 		spin_unlock(&vcpu->kvm->mmu_lock);
 		up_read(&vcpu->kvm->slots_lock);
 		return 1;
 	}

 	++vcpu->stat.pf_fixed;
 	kvm_mmu_audit(vcpu, "post page fault (fixed)");
 	spin_unlock(&vcpu->kvm->mmu_lock);
 	up_read(&vcpu->kvm->slots_lock);

 	return write_pt;
 }

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

 	r = FNAME(walk_addr)(&walker, vcpu, vaddr, 0, 0, 0);

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

 	return gpa;
 }

 static void FNAME(prefetch_page)(struct kvm_vcpu *vcpu,
 				 struct kvm_mmu_page *sp)
 {
 	int i, offset = 0, r = 0;
 	pt_element_t pt;

 	if (sp->role.metaphysical
 	    || (PTTYPE == 32 && sp->role.level > PT_PAGE_TABLE_LEVEL)) {
 		nonpaging_prefetch_page(vcpu, sp);
 		return;
 	}

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

 	for (i = 0; i < PT64_ENT_PER_PAGE; ++i) {
 		gpa_t pte_gpa = gfn_to_gpa(sp->gfn);
 		pte_gpa += (i+offset) * sizeof(pt_element_t);

 		r = kvm_read_guest_atomic(vcpu->kvm, pte_gpa, &pt,
 					  sizeof(pt_element_t));
 		if (r || is_present_pte(pt))
 			sp->spt[i] = shadow_trap_nonpresent_pte;
 		else
 			sp->spt[i] = shadow_notrap_nonpresent_pte;
 	}
 }

 #undef pt_element_t
 #undef guest_walker
 #undef FNAME
 #undef PT_BASE_ADDR_MASK
 #undef PT_INDEX
 #undef SHADOW_PT_INDEX
 #undef PT_LEVEL_MASK
 #undef PT_DIR_BASE_ADDR_MASK
 #undef PT_LEVEL_BITS
 #undef PT_MAX_FULL_LEVELS
 #undef gpte_to_gfn
 #undef gpte_to_gfn_pde
 #undef CMPXCHG
	/*
	* 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.
	*
	* 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_DIR_BASE_ADDR_MASK PT64_DIR_BASE_ADDR_MASK
	#define PT_INDEX(addr, level) PT64_INDEX(addr, level)
	#define SHADOW_PT_INDEX(addr, level) PT64_INDEX(addr, level)
	#define PT_LEVEL_MASK(level) PT64_LEVEL_MASK(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_DIR_BASE_ADDR_MASK PT32_DIR_BASE_ADDR_MASK
	#define PT_INDEX(addr, level) PT32_INDEX(addr, level)
	#define SHADOW_PT_INDEX(addr, level) PT64_INDEX(addr, level)
	#define PT_LEVEL_MASK(level) PT32_LEVEL_MASK(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 FNAME(gpte_to_gfn)
	#define gpte_to_gfn_pde FNAME(gpte_to_gfn_pde)

	/*
	* The guest_walker structure emulates the behavior of the hardware page
	* table walker.
	*/
	struct guest_walker {
	int level;
	gfn_t table_gfn[PT_MAX_FULL_LEVELS];
	pt_element_t ptes[PT_MAX_FULL_LEVELS];
	gpa_t pte_gpa[PT_MAX_FULL_LEVELS];
	unsigned pt_access;
	unsigned pte_access;
	gfn_t gfn;
	u32 error_code;
	};

	static gfn_t gpte_to_gfn(pt_element_t gpte)
	{
	return (gpte & PT_BASE_ADDR_MASK) >> PAGE_SHIFT;
	}

	static gfn_t gpte_to_gfn_pde(pt_element_t gpte)
	{
	return (gpte & PT_DIR_BASE_ADDR_MASK) >> PAGE_SHIFT;
	}

	static bool FNAME(cmpxchg_gpte)(struct kvm *kvm,
	gfn_t table_gfn, unsigned index,
	pt_element_t orig_pte, pt_element_t new_pte)
	{
	pt_element_t ret;
	pt_element_t *table;
	struct page *page;

	down_read(&current->mm->mmap_sem);
	page = gfn_to_page(kvm, table_gfn);
	up_read(&current->mm->mmap_sem);

	table = kmap_atomic(page, KM_USER0);

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

	kunmap_atomic(table, KM_USER0);

	kvm_release_page_dirty(page);

	return (ret != orig_pte);
	}

	static unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu, pt_element_t gpte)
	{
	unsigned access;

	access = (gpte & (PT_WRITABLE_MASK \| PT_USER_MASK)) \| ACC_EXEC_MASK;
	#if PTTYPE == 64
	if (is_nx(vcpu))
	access &= ~(gpte >> PT64_NX_SHIFT);
	#endif
	return access;
	}

	/*
	* Fetch a guest pte for a guest virtual address
	*/
	static int FNAME(walk_addr)(struct guest_walker *walker,
	struct kvm_vcpu *vcpu, gva_t addr,
	int write_fault, int user_fault, int fetch_fault)
	{
	pt_element_t pte;
	gfn_t table_gfn;
	unsigned index, pt_access, pte_access;
	gpa_t pte_gpa;

	pgprintk("%s: addr %lx\n", __FUNCTION__, addr);
	walk:
	walker->level = vcpu->arch.mmu.root_level;
	pte = vcpu->arch.cr3;
	#if PTTYPE == 64
	if (!is_long_mode(vcpu)) {
	pte = vcpu->arch.pdptrs[(addr >> 30) & 3];
	if (!is_present_pte(pte))
	goto not_present;
	--walker->level;
	}
	#endif
	ASSERT((!is_long_mode(vcpu) && is_pae(vcpu)) \|\|
	(vcpu->arch.cr3 & CR3_NONPAE_RESERVED_BITS) == 0);

	pt_access = ACC_ALL;

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

	table_gfn = gpte_to_gfn(pte);
	pte_gpa = gfn_to_gpa(table_gfn);
	pte_gpa += index * sizeof(pt_element_t);
	walker->table_gfn[walker->level - 1] = table_gfn;
	walker->pte_gpa[walker->level - 1] = pte_gpa;
	pgprintk("%s: table_gfn[%d] %lx\n", __FUNCTION__,
	walker->level - 1, table_gfn);

	kvm_read_guest(vcpu->kvm, pte_gpa, &pte, sizeof(pte));

	if (!is_present_pte(pte))
	goto not_present;

	if (write_fault && !is_writeble_pte(pte))
	if (user_fault \|\| is_write_protection(vcpu))
	goto access_error;

	if (user_fault && !(pte & PT_USER_MASK))
	goto access_error;

	#if PTTYPE == 64
	if (fetch_fault && is_nx(vcpu) && (pte & PT64_NX_MASK))
	goto access_error;
	#endif

	if (!(pte & PT_ACCESSED_MASK)) {
	mark_page_dirty(vcpu->kvm, table_gfn);
	if (FNAME(cmpxchg_gpte)(vcpu->kvm, table_gfn,
	index, pte, pte\|PT_ACCESSED_MASK))
	goto walk;
	pte \|= PT_ACCESSED_MASK;
	}

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

	walker->ptes[walker->level - 1] = pte;

	if (walker->level == PT_PAGE_TABLE_LEVEL) {
	walker->gfn = gpte_to_gfn(pte);
	break;
	}

	if (walker->level == PT_DIRECTORY_LEVEL
	&& (pte & PT_PAGE_SIZE_MASK)
	&& (PTTYPE == 64 \|\| is_pse(vcpu))) {
	walker->gfn = gpte_to_gfn_pde(pte);
	walker->gfn += PT_INDEX(addr, PT_PAGE_TABLE_LEVEL);
	if (PTTYPE == 32 && is_cpuid_PSE36())
	walker->gfn += pse36_gfn_delta(pte);
	break;
	}

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

	if (write_fault && !is_dirty_pte(pte)) {
	bool ret;

	mark_page_dirty(vcpu->kvm, table_gfn);
	ret = FNAME(cmpxchg_gpte)(vcpu->kvm, table_gfn, index, pte,
	pte\|PT_DIRTY_MASK);
	if (ret)
	goto walk;
	pte \|= PT_DIRTY_MASK;
	kvm_mmu_pte_write(vcpu, pte_gpa, (u8 *)&pte, sizeof(pte));
	walker->ptes[walker->level - 1] = pte;
	}

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

	not_present:
	walker->error_code = 0;
	goto err;

	access_error:
	walker->error_code = PFERR_PRESENT_MASK;

	err:
	if (write_fault)
	walker->error_code \|= PFERR_WRITE_MASK;
	if (user_fault)
	walker->error_code \|= PFERR_USER_MASK;
	if (fetch_fault)
	walker->error_code \|= PFERR_FETCH_MASK;
	return 0;
	}

	static void FNAME(update_pte)(struct kvm_vcpu vcpu, struct kvm_mmu_page page,
	u64 spte, const void pte, int bytes,
	int offset_in_pte)
	{
	pt_element_t gpte;
	unsigned pte_access;
	struct page *npage;

	gpte = (const pt_element_t )pte;
	if (~gpte & (PT_PRESENT_MASK \| PT_ACCESSED_MASK)) {
	if (!offset_in_pte && !is_present_pte(gpte))
	set_shadow_pte(spte, shadow_notrap_nonpresent_pte);
	return;
	}
	if (bytes < sizeof(pt_element_t))
	return;
	pgprintk("%s: gpte %llx spte %p\n", __FUNCTION__, (u64)gpte, spte);
	pte_access = page->role.access & FNAME(gpte_access)(vcpu, gpte);
	if (gpte_to_gfn(gpte) != vcpu->arch.update_pte.gfn)
	return;
	npage = vcpu->arch.update_pte.page;
	if (!npage)
	return;
	get_page(npage);
	mmu_set_spte(vcpu, spte, page->role.access, pte_access, 0, 0,
	gpte & PT_DIRTY_MASK, NULL, gpte_to_gfn(gpte), npage);
	}

	/*
	* Fetch a shadow pte for a specific level in the paging hierarchy.
	*/
	static u64 FNAME(fetch)(struct kvm_vcpu vcpu, gva_t addr,
	struct guest_walker *walker,
	int user_fault, int write_fault, int *ptwrite,
	struct page *page)
	{
	hpa_t shadow_addr;
	int level;
	u64 *shadow_ent;
	unsigned access = walker->pt_access;

	if (!is_present_pte(walker->ptes[walker->level - 1]))
	return NULL;

	shadow_addr = vcpu->arch.mmu.root_hpa;
	level = vcpu->arch.mmu.shadow_root_level;
	if (level == PT32E_ROOT_LEVEL) {
	shadow_addr = vcpu->arch.mmu.pae_root[(addr >> 30) & 3];
	shadow_addr &= PT64_BASE_ADDR_MASK;
	--level;
	}

	for (; ; level--) {
	u32 index = SHADOW_PT_INDEX(addr, level);
	struct kvm_mmu_page *shadow_page;
	u64 shadow_pte;
	int metaphysical;
	gfn_t table_gfn;

	shadow_ent = ((u64 *)__va(shadow_addr)) + index;
	if (level == PT_PAGE_TABLE_LEVEL)
	break;
	if (is_shadow_present_pte(*shadow_ent)) {
	shadow_addr = *shadow_ent & PT64_BASE_ADDR_MASK;
	continue;
	}

	if (level - 1 == PT_PAGE_TABLE_LEVEL
	&& walker->level == PT_DIRECTORY_LEVEL) {
	metaphysical = 1;
	if (!is_dirty_pte(walker->ptes[level - 1]))
	access &= ~ACC_WRITE_MASK;
	table_gfn = gpte_to_gfn(walker->ptes[level - 1]);
	} else {
	metaphysical = 0;
	table_gfn = walker->table_gfn[level - 2];
	}
	shadow_page = kvm_mmu_get_page(vcpu, table_gfn, addr, level-1,
	metaphysical, access,
	shadow_ent);
	if (!metaphysical) {
	int r;
	pt_element_t curr_pte;
	r = kvm_read_guest_atomic(vcpu->kvm,
	walker->pte_gpa[level - 2],
	&curr_pte, sizeof(curr_pte));
	if (r \|\| curr_pte != walker->ptes[level - 2]) {
	kvm_release_page_clean(page);
	return NULL;
	}
	}
	shadow_addr = __pa(shadow_page->spt);
	shadow_pte = shadow_addr \| PT_PRESENT_MASK \| PT_ACCESSED_MASK
	\| PT_WRITABLE_MASK \| PT_USER_MASK;
	*shadow_ent = shadow_pte;
	}

	mmu_set_spte(vcpu, shadow_ent, access, walker->pte_access & access,
	user_fault, write_fault,
	walker->ptes[walker->level-1] & PT_DIRTY_MASK,
	ptwrite, walker->gfn, page);

	return shadow_ent;
	}

	/*
	* 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)
	{
	int write_fault = error_code & PFERR_WRITE_MASK;
	int user_fault = error_code & PFERR_USER_MASK;
	int fetch_fault = error_code & PFERR_FETCH_MASK;
	struct guest_walker walker;
	u64 *shadow_pte;
	int write_pt = 0;
	int r;
	struct page *page;

	pgprintk("%s: addr %lx err %x\n", __FUNCTION__, addr, error_code);
	kvm_mmu_audit(vcpu, "pre page fault");

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

	down_read(&vcpu->kvm->slots_lock);
	/*
	* Look up the shadow pte for the faulting address.
	*/
	r = FNAME(walk_addr)(&walker, vcpu, addr, write_fault, user_fault,
	fetch_fault);

	/*
	* The page is not mapped by the guest. Let the guest handle it.
	*/
	if (!r) {
	pgprintk("%s: guest page fault\n", __FUNCTION__);
	inject_page_fault(vcpu, addr, walker.error_code);
	vcpu->arch.last_pt_write_count = 0; /* reset fork detector */
	up_read(&vcpu->kvm->slots_lock);
	return 0;
	}

	down_read(&current->mm->mmap_sem);
	page = gfn_to_page(vcpu->kvm, walker.gfn);
	up_read(&current->mm->mmap_sem);

	spin_lock(&vcpu->kvm->mmu_lock);
	kvm_mmu_free_some_pages(vcpu);
	shadow_pte = FNAME(fetch)(vcpu, addr, &walker, user_fault, write_fault,
	&write_pt, page);
	pgprintk("%s: shadow pte %p %llx ptwrite %d\n", __FUNCTION__,
	shadow_pte, *shadow_pte, write_pt);

	if (!write_pt)
	vcpu->arch.last_pt_write_count = 0; /* reset fork detector */

	/*
	* mmio: emulate if accessible, otherwise its a guest fault.
	*/
	if (shadow_pte && is_io_pte(*shadow_pte)) {
	spin_unlock(&vcpu->kvm->mmu_lock);
	up_read(&vcpu->kvm->slots_lock);
	return 1;
	}

	++vcpu->stat.pf_fixed;
	kvm_mmu_audit(vcpu, "post page fault (fixed)");
	spin_unlock(&vcpu->kvm->mmu_lock);
	up_read(&vcpu->kvm->slots_lock);

	return write_pt;
	}

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

	r = FNAME(walk_addr)(&walker, vcpu, vaddr, 0, 0, 0);

	if (r) {
	gpa = gfn_to_gpa(walker.gfn);
	gpa \|= vaddr & ~PAGE_MASK;
	}

	return gpa;
	}

	static void FNAME(prefetch_page)(struct kvm_vcpu *vcpu,
	struct kvm_mmu_page *sp)
	{
	int i, offset = 0, r = 0;
	pt_element_t pt;

	if (sp->role.metaphysical
	\|\| (PTTYPE == 32 && sp->role.level > PT_PAGE_TABLE_LEVEL)) {
	nonpaging_prefetch_page(vcpu, sp);
	return;
	}

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

	for (i = 0; i < PT64_ENT_PER_PAGE; ++i) {
	gpa_t pte_gpa = gfn_to_gpa(sp->gfn);
	pte_gpa += (i+offset) * sizeof(pt_element_t);

	r = kvm_read_guest_atomic(vcpu->kvm, pte_gpa, &pt,
	sizeof(pt_element_t));
	if (r \|\| is_present_pte(pt))
	sp->spt[i] = shadow_trap_nonpresent_pte;
	else
	sp->spt[i] = shadow_notrap_nonpresent_pte;
	}
	}

	#undef pt_element_t
	#undef guest_walker
	#undef FNAME
	#undef PT_BASE_ADDR_MASK
	#undef PT_INDEX
	#undef SHADOW_PT_INDEX
	#undef PT_LEVEL_MASK
	#undef PT_DIR_BASE_ADDR_MASK
	#undef PT_LEVEL_BITS
	#undef PT_MAX_FULL_LEVELS
	#undef gpte_to_gfn
	#undef gpte_to_gfn_pde
	#undef CMPXCHG