[PATCH v3 1/6] KVM: x86/mmu: Set lpage_disallowed in TDP MMU before setting SPTE

[Mingwei Zhang]

From: Sean Christopherson <seanjc@xxxxxxxxxx>

Set lpage_disallowed in TDP MMU shadow pages before making the SP visible
to other readers, i.e. before setting its SPTE.  This will allow KVM to
query lpage_disallowed when determining if a shadow page can be replaced
by a NX huge page without violating the rules of the mitigation.

Reviewed-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kvm/mmu/mmu.c          | 14 ++++++++++----
 arch/x86/kvm/mmu/mmu_internal.h |  2 +-
 arch/x86/kvm/mmu/tdp_mmu.c      | 20 ++++++++++++--------
 3 files changed, 23 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 1361eb4599b4..5cb845fae56e 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -812,14 +812,20 @@ static void account_shadowed(struct kvm *kvm, struct kvm_mmu_page *sp)
 	kvm_mmu_gfn_disallow_lpage(slot, gfn);
 }
 
-void account_huge_nx_page(struct kvm *kvm, struct kvm_mmu_page *sp)
+void __account_huge_nx_page(struct kvm *kvm, struct kvm_mmu_page *sp)
 {
-	if (sp->lpage_disallowed)
-		return;
-
 	++kvm->stat.nx_lpage_splits;
 	list_add_tail(&sp->lpage_disallowed_link,
 		      &kvm->arch.lpage_disallowed_mmu_pages);
+}
+
+static void account_huge_nx_page(struct kvm *kvm, struct kvm_mmu_page *sp)
+{
+	if (sp->lpage_disallowed)
+		return;
+
+	__account_huge_nx_page(kvm, sp);
+
 	sp->lpage_disallowed = true;
 }
 
diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index 1bff453f7cbe..4a0087efa1e3 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -168,7 +168,7 @@ void disallowed_hugepage_adjust(struct kvm_page_fault *fault, u64 spte, int cur_
 
 void *mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
 
-void account_huge_nx_page(struct kvm *kvm, struct kvm_mmu_page *sp);
+void __account_huge_nx_page(struct kvm *kvm, struct kvm_mmu_page *sp);
 void unaccount_huge_nx_page(struct kvm *kvm, struct kvm_mmu_page *sp);
 
 #endif /* __KVM_X86_MMU_INTERNAL_H */
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index b3b6426725d4..f05423545e6d 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1122,16 +1122,13 @@ static int tdp_mmu_map_handle_target_level(struct kvm_vcpu *vcpu,
  * @kvm: kvm instance
  * @iter: a tdp_iter instance currently on the SPTE that should be set
  * @sp: The new TDP page table to install.
- * @account_nx: True if this page table is being installed to split a
- *              non-executable huge page.
  * @shared: This operation is running under the MMU lock in read mode.
  *
  * Returns: 0 if the new page table was installed. Non-0 if the page table
  *          could not be installed (e.g. the atomic compare-exchange failed).
  */
 static int tdp_mmu_link_sp(struct kvm *kvm, struct tdp_iter *iter,
-			   struct kvm_mmu_page *sp, bool account_nx,
-			   bool shared)
+			   struct kvm_mmu_page *sp, bool shared)
 {
 	u64 spte = make_nonleaf_spte(sp->spt, !shadow_accessed_mask);
 	int ret = 0;
@@ -1146,8 +1143,6 @@ static int tdp_mmu_link_sp(struct kvm *kvm, struct tdp_iter *iter,
 
 	spin_lock(&kvm->arch.tdp_mmu_pages_lock);
 	list_add(&sp->link, &kvm->arch.tdp_mmu_pages);
-	if (account_nx)
-		account_huge_nx_page(kvm, sp);
 	spin_unlock(&kvm->arch.tdp_mmu_pages_lock);
 
 	return 0;
@@ -1160,6 +1155,7 @@ static int tdp_mmu_link_sp(struct kvm *kvm, struct tdp_iter *iter,
 int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 {
 	struct kvm_mmu *mmu = vcpu->arch.mmu;
+	struct kvm *kvm = vcpu->kvm;
 	struct tdp_iter iter;
 	struct kvm_mmu_page *sp;
 	int ret;
@@ -1210,10 +1206,18 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 			sp = tdp_mmu_alloc_sp(vcpu);
 			tdp_mmu_init_child_sp(sp, &iter);
 
-			if (tdp_mmu_link_sp(vcpu->kvm, &iter, sp, account_nx, true)) {
+			sp->lpage_disallowed = account_nx;
+
+			if (tdp_mmu_link_sp(kvm, &iter, sp, true)) {
 				tdp_mmu_free_sp(sp);
 				break;
 			}
+
+			if (account_nx) {
+				spin_lock(&kvm->arch.tdp_mmu_pages_lock);
+				__account_huge_nx_page(kvm, sp);
+				spin_unlock(&kvm->arch.tdp_mmu_pages_lock);
+			}
 		}
 	}
 
@@ -1501,7 +1505,7 @@ static int tdp_mmu_split_huge_page(struct kvm *kvm, struct tdp_iter *iter,
 	 * correctness standpoint since the translation will be the same either
 	 * way.
 	 */
-	ret = tdp_mmu_link_sp(kvm, iter, sp, false, shared);
+	ret = tdp_mmu_link_sp(kvm, iter, sp, shared);
 	if (ret)
 		goto out;
 
-- 
2.35.1.1094.g7c7d902a7c-goog