linux-kernel - [PATCH 22/22] kvm: mmu: Don't clear write flooding count for direct roots

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Date:   Fri, 25 Sep 2020 14:23:02 -0700
From:   Ben Gardon <bgardon@...gle.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Cannon Matthews <cannonmatthews@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Peter Shier <pshier@...gle.com>,
        Peter Feiner <pfeiner@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Yulei Zhang <yulei.kernel@...il.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: [PATCH 22/22] kvm: mmu: Don't clear write flooding count for direct roots

Direct roots don't have a write flooding count because the guest can't
affect that paging structure. Thus there's no need to clear the write
flooding count on a fast CR3 switch for direct roots.

Tested by running kvm-unit-tests and KVM selftests on an Intel Haswell
machine. This series introduced no new failures.

This series can be viewed in Gerrit at:
	https://linux-review.googlesource.com/c/virt/kvm/kvm/+/2538

Signed-off-by: Ben Gardon <bgardon@...gle.com>
---
 arch/x86/kvm/mmu/mmu.c     | 15 +++++++++++----
 arch/x86/kvm/mmu/tdp_mmu.c | 12 ++++++++++++
 arch/x86/kvm/mmu/tdp_mmu.h |  2 ++
 3 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 0ce7720a72d4e..345c934fabf4c 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4267,7 +4267,8 @@ static void nonpaging_init_context(struct kvm_vcpu *vcpu,
 	context->nx = false;
 }
 
-static inline bool is_root_usable(struct kvm_mmu_root_info *root, gpa_t pgd,
+static inline bool is_root_usable(struct kvm *kvm,
+				  struct kvm_mmu_root_info *root, gpa_t pgd,
 				  union kvm_mmu_page_role role)
 {
 	return (role.direct || pgd == root->pgd) &&
@@ -4293,13 +4294,13 @@ static bool cached_root_available(struct kvm_vcpu *vcpu, gpa_t new_pgd,
 	root.pgd = mmu->root_pgd;
 	root.hpa = mmu->root_hpa;
 
-	if (is_root_usable(&root, new_pgd, new_role))
+	if (is_root_usable(vcpu->kvm, &root, new_pgd, new_role))
 		return true;
 
 	for (i = 0; i < KVM_MMU_NUM_PREV_ROOTS; i++) {
 		swap(root, mmu->prev_roots[i]);
 
-		if (is_root_usable(&root, new_pgd, new_role))
+		if (is_root_usable(vcpu->kvm, &root, new_pgd, new_role))
 			break;
 	}
 
@@ -4356,7 +4357,13 @@ static void __kvm_mmu_new_pgd(struct kvm_vcpu *vcpu, gpa_t new_pgd,
 	 */
 	vcpu_clear_mmio_info(vcpu, MMIO_GVA_ANY);
 
-	__clear_sp_write_flooding_count(to_shadow_page(vcpu->arch.mmu->root_hpa));
+	/*
+	 * If this is a direct root page, it doesn't have a write flooding
+	 * count. Otherwise, clear the write flooding count.
+	 */
+	if (!new_role.direct)
+		__clear_sp_write_flooding_count(
+				to_shadow_page(vcpu->arch.mmu->root_hpa));
 }
 
 void kvm_mmu_new_pgd(struct kvm_vcpu *vcpu, gpa_t new_pgd, bool skip_tlb_flush,
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 42dde27decd75..c07831b0c73e1 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -124,6 +124,18 @@ static struct kvm_mmu_page *find_tdp_mmu_root_with_role(
 	return NULL;
 }
 
+hpa_t kvm_tdp_mmu_root_hpa_for_role(struct kvm *kvm,
+				    union kvm_mmu_page_role role)
+{
+	struct kvm_mmu_page *root;
+
+	root = find_tdp_mmu_root_with_role(kvm, role);
+	if (root)
+		return __pa(root->spt);
+
+	return INVALID_PAGE;
+}
+
 static union kvm_mmu_page_role page_role_for_level(struct kvm_vcpu *vcpu,
 						   int level)
 {
diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
index cc0b7241975aa..2395ffa71bb05 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.h
+++ b/arch/x86/kvm/mmu/tdp_mmu.h
@@ -9,6 +9,8 @@ void kvm_mmu_init_tdp_mmu(struct kvm *kvm);
 void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm);
 
 bool is_tdp_mmu_root(struct kvm *kvm, hpa_t root);
+hpa_t kvm_tdp_mmu_root_hpa_for_role(struct kvm *kvm,
+				    union kvm_mmu_page_role role);
 hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu);
 void kvm_tdp_mmu_put_root_hpa(struct kvm *kvm, hpa_t root_hpa);
 
-- 
2.28.0.709.gb0816b6eb0-goog