linux-kernel - [PATCH 2/5] KVM: nSVM: fix few bugs in the vmcb02 caching logic

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Message-Id: <20210503125446.1353307-3-mlevitsk@redhat.com>
Date:   Mon,  3 May 2021 15:54:43 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org (open list:X86 ARCHITECTURE (32-BIT AND
        64-BIT)), Jim Mattson <jmattson@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Joerg Roedel <joro@...tes.org>, Ingo Molnar <mingo@...hat.com>,
        x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        Sean Christopherson <seanjc@...gle.com>,
        Cathy Avery <cavery@...hat.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH 2/5] KVM: nSVM: fix few bugs in the vmcb02 caching logic

* Define and use an invalid GPA (all ones) for init value of last
  and current nested vmcb physical addresses.

* Reset the current vmcb12 gpa to the invalid value when leaving
  the nested mode, similar to what is done on nested vmexit.

* Reset	the last seen vmcb12 address when disabling the nested SVM,
  as it relies on vmcb02 fields which are freed at that point.

Fixes: 4995a3685f1b ("KVM: SVM: Use a separate vmcb for the nested L2 guest")

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/svm/nested.c       | 11 +++++++++++
 arch/x86/kvm/svm/svm.c          |  4 ++--
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 3e5fc80a35c8..4b95e7c4a4e3 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -113,6 +113,7 @@
 #define VALID_PAGE(x) ((x) != INVALID_PAGE)
 
 #define UNMAPPED_GVA (~(gpa_t)0)
+#define INVALID_GPA (~(gpa_t)0)
 
 /* KVM Hugepage definitions for x86 */
 #define KVM_MAX_HUGEPAGE_LEVEL	PG_LEVEL_1G
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 3321220f3deb..a88c64e004c3 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -872,6 +872,15 @@ void svm_free_nested(struct vcpu_svm *svm)
 	__free_page(virt_to_page(svm->nested.vmcb02.ptr));
 	svm->nested.vmcb02.ptr = NULL;
 
+	/*
+	 * When last_vmcb12_gpa matches the current vmcb12 gpa,
+	 * some vmcb12 fields are not loaded if they are marked clean
+	 * in the vmcb12, since in this case they are up to date already.
+	 *
+	 * When the vmcb02 is freed, this optimization becomes invalid.
+	 */
+	svm->nested.last_vmcb12_gpa = INVALID_GPA;
+
 	svm->nested.initialized = false;
 }
 
@@ -884,6 +893,8 @@ void svm_leave_nested(struct vcpu_svm *svm)
 
 	if (is_guest_mode(vcpu)) {
 		svm->nested.nested_run_pending = 0;
+		svm->nested.vmcb12_gpa = INVALID_GPA;
+
 		leave_guest_mode(vcpu);
 
 		svm_switch_vmcb(svm, &svm->vmcb01);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index a7271f31df47..987173e1f954 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1235,8 +1235,8 @@ static void init_vmcb(struct kvm_vcpu *vcpu)
 	svm->current_vmcb->asid_generation = 0;
 	svm->asid = 0;
 
-	svm->nested.vmcb12_gpa = 0;
-	svm->nested.last_vmcb12_gpa = 0;
+	svm->nested.vmcb12_gpa = INVALID_GPA;
+	svm->nested.last_vmcb12_gpa = INVALID_GPA;
 	vcpu->arch.hflags = 0;
 
 	if (!kvm_pause_in_guest(vcpu->kvm)) {
-- 
2.26.2