KVM: MMU: rename has_wrprotected_page to mmu_gfn_lpage_is_disallowed

kvm_lpage_info->write_count is used to detect if the large page mapping
for the gfn on the specified level is allowed, rename it to disallow_lpage
to reflect its purpose, also we rename has_wrprotected_page() to
mmu_gfn_lpage_is_disallowed() to make the code more clearer

Later we will extend this mechanism for page tracking: if the gfn is
tracked then large mapping for that gfn on any level is not allowed.
The new name is more straightforward
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

CVE-2018-12207

(cherry picked from commit 92f94f1e)
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

Documentation/virtual/kvm/mmu.txt

@@ -392,11 +392,11 @@ To instantiate a large spte, four constraints must be satisfied:
   write-protected pages
 - the guest page must be wholly contained by a single memory slot
 
-To check the last two conditions, the mmu maintains a ->write_count set of
+To check the last two conditions, the mmu maintains a ->disallow_lpage set of
 arrays for each memory slot and large page size.  Every write protected page
-causes its write_count to be incremented, thus preventing instantiation of
+causes its disallow_lpage to be incremented, thus preventing instantiation of
 a large spte.  The frames at the end of an unaligned memory slot have
-artificially inflated ->write_counts so they can never be instantiated.
+artificially inflated ->disallow_lpages so they can never be instantiated.
 
 Zapping all pages (page generation count)
 =========================================

arch/x86/include/asm/kvm_host.h

@@ -624,7 +624,7 @@ struct kvm_vcpu_arch {
 };
 
 struct kvm_lpage_info {
-	int write_count;
+	int disallow_lpage;
 };
 
 struct kvm_arch_memory_slot {

arch/x86/kvm/mmu.c

@@ -794,7 +794,7 @@ static void account_shadowed(struct kvm *kvm, struct kvm_mmu_page *sp)
 	slot = __gfn_to_memslot(slots, gfn);
 	for (i = PT_DIRECTORY_LEVEL; i <= PT_MAX_HUGEPAGE_LEVEL; ++i) {
 		linfo = lpage_info_slot(gfn, slot, i);
-		linfo->write_count += 1;
+		linfo->disallow_lpage += 1;
 	}
 	kvm->arch.indirect_shadow_pages++;
 }
@@ -812,31 +812,32 @@ static void unaccount_shadowed(struct kvm *kvm, struct kvm_mmu_page *sp)
 	slot = __gfn_to_memslot(slots, gfn);
 	for (i = PT_DIRECTORY_LEVEL; i <= PT_MAX_HUGEPAGE_LEVEL; ++i) {
 		linfo = lpage_info_slot(gfn, slot, i);
-		linfo->write_count -= 1;
-		WARN_ON(linfo->write_count < 0);
+		linfo->disallow_lpage -= 1;
+		WARN_ON(linfo->disallow_lpage < 0);
 	}
 	kvm->arch.indirect_shadow_pages--;
 }
 
-static int __has_wrprotected_page(gfn_t gfn, int level,
-				  struct kvm_memory_slot *slot)
+static bool __mmu_gfn_lpage_is_disallowed(gfn_t gfn, int level,
+					  struct kvm_memory_slot *slot)
 {
 	struct kvm_lpage_info *linfo;
 
 	if (slot) {
 		linfo = lpage_info_slot(gfn, slot, level);
-		return linfo->write_count;
+		return !!linfo->disallow_lpage;
 	}
 
-	return 1;
+	return true;
 }
 
-static int has_wrprotected_page(struct kvm_vcpu *vcpu, gfn_t gfn, int level)
+static bool mmu_gfn_lpage_is_disallowed(struct kvm_vcpu *vcpu, gfn_t gfn,
+					int level)
 {
 	struct kvm_memory_slot *slot;
 
 	slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
-	return __has_wrprotected_page(gfn, level, slot);
+	return __mmu_gfn_lpage_is_disallowed(gfn, level, slot);
 }
 
 static int host_mapping_level(struct kvm *kvm, gfn_t gfn)
@@ -902,7 +903,7 @@ static int mapping_level(struct kvm_vcpu *vcpu, gfn_t large_gfn,
 	max_level = min(kvm_x86_ops->get_lpage_level(), host_level);
 
 	for (level = PT_DIRECTORY_LEVEL; level <= max_level; ++level)
-		if (__has_wrprotected_page(large_gfn, level, slot))
+		if (__mmu_gfn_lpage_is_disallowed(large_gfn, level, slot))
 			break;
 
 	return level - 1;
@@ -2532,7 +2533,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 		 * be fixed if guest refault.
 		 */
 		if (level > PT_PAGE_TABLE_LEVEL &&
-		    has_wrprotected_page(vcpu, gfn, level))
+		    mmu_gfn_lpage_is_disallowed(vcpu, gfn, level))
 			goto done;
 
 		spte |= PT_WRITABLE_MASK | SPTE_MMU_WRITEABLE;
@@ -2797,7 +2798,7 @@ static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu,
 	if (!is_error_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn) &&
 	    level == PT_PAGE_TABLE_LEVEL &&
 	    PageTransCompound(pfn_to_page(pfn)) &&
-	    !has_wrprotected_page(vcpu, gfn, PT_DIRECTORY_LEVEL)) {
+	    !mmu_gfn_lpage_is_disallowed(vcpu, gfn, PT_DIRECTORY_LEVEL)) {
 		unsigned long mask;
 		/*
 		 * mmu_notifier_retry was successful and we hold the

arch/x86/kvm/x86.c

@@ -8132,6 +8132,7 @@ int kvm_arch_create_memslot(struct kvm *kvm, struct kvm_memory_slot *slot,
 	int i;
 
 	for (i = 0; i < KVM_NR_PAGE_SIZES; ++i) {
+		struct kvm_lpage_info *linfo;
 		unsigned long ugfn;
 		int lpages;
 		int level = i + 1;
@@ -8146,15 +8147,16 @@ int kvm_arch_create_memslot(struct kvm *kvm, struct kvm_memory_slot *slot,
 		if (i == 0)
 			continue;
 
-		slot->arch.lpage_info[i - 1] = kvm_kvzalloc(lpages *
-					sizeof(*slot->arch.lpage_info[i - 1]));
-		if (!slot->arch.lpage_info[i - 1])
+		linfo = kvm_kvzalloc(lpages * sizeof(*linfo));
+		if (!linfo)
 			goto out_free;
 
+		slot->arch.lpage_info[i - 1] = linfo;
+
 		if (slot->base_gfn & (KVM_PAGES_PER_HPAGE(level) - 1))
-			slot->arch.lpage_info[i - 1][0].write_count = 1;
+			linfo[0].disallow_lpage = 1;
 		if ((slot->base_gfn + npages) & (KVM_PAGES_PER_HPAGE(level) - 1))
-			slot->arch.lpage_info[i - 1][lpages - 1].write_count = 1;
+			linfo[lpages - 1].disallow_lpage = 1;
 		ugfn = slot->userspace_addr >> PAGE_SHIFT;
 		/*
 		 * If the gfn and userspace address are not aligned wrt each
@@ -8166,7 +8168,7 @@ int kvm_arch_create_memslot(struct kvm *kvm, struct kvm_memory_slot *slot,
 			unsigned long j;
 
 			for (j = 0; j < lpages; ++j)
-				slot->arch.lpage_info[i - 1][j].write_count = 1;
+				linfo[j].disallow_lpage = 1;
 		}
 	}