[25/30] KVM: nSVM: leave guest mode when clearing EFER.SVME
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Message ID 20200529153934.11694-26-pbonzini@redhat.com
State In Next
Commit c513f484c5582a8efadf3d72298e2285b041536e
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Series
  • KVM: nSVM: event fixes and migration support
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Commit Message

Paolo Bonzini May 29, 2020, 3:39 p.m. UTC
According to the AMD manual, the effect of turning off EFER.SVME while a
guest is running is undefined.  We make it leave guest mode immediately,
similar to the effect of clearing the VMX bit in MSR_IA32_FEAT_CTL.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/svm/nested.c | 16 ++++++++++++++++
 arch/x86/kvm/svm/svm.c    | 10 ++++++++--
 arch/x86/kvm/svm/svm.h    |  1 +
 3 files changed, 25 insertions(+), 2 deletions(-)

Comments

Krish Sadhukhan June 1, 2020, 2:26 a.m. UTC | #1
On 5/29/20 8:39 AM, Paolo Bonzini wrote:
> According to the AMD manual, the effect of turning off EFER.SVME while a
> guest is running is undefined.  We make it leave guest mode immediately,
> similar to the effect of clearing the VMX bit in MSR_IA32_FEAT_CTL.


I see that svm_set_efer() is called in enter_svm_guest_mode() and 
nested_svm_vmexit(). In the VMRUN path, we have already checked 
EFER.SVME in nested_vmcb_checks(). So if it was not set, we wouldn't 
come to enter_svm_guest_mode(). Your fix is only for the #VMEXIT path then ?

>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   arch/x86/kvm/svm/nested.c | 16 ++++++++++++++++
>   arch/x86/kvm/svm/svm.c    | 10 ++++++++--
>   arch/x86/kvm/svm/svm.h    |  1 +
>   3 files changed, 25 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index bd3a89cd4070..369eca73fe3e 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -618,6 +618,22 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
>   	return 0;
>   }
>   
> +/*
> + * Forcibly leave nested mode in order to be able to reset the VCPU later on.
> + */
> +void svm_leave_nested(struct vcpu_svm *svm)
> +{
> +	if (is_guest_mode(&svm->vcpu)) {
> +		struct vmcb *hsave = svm->nested.hsave;
> +		struct vmcb *vmcb = svm->vmcb;
> +
> +		svm->nested.nested_run_pending = 0;
> +		leave_guest_mode(&svm->vcpu);
> +		copy_vmcb_control_area(&vmcb->control, &hsave->control);
> +		nested_svm_uninit_mmu_context(&svm->vcpu);
> +	}
> +}
> +
>   static int nested_svm_exit_handled_msr(struct vcpu_svm *svm)
>   {
>   	u32 offset, msr, value;
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index bc08221f6743..b4db9a980469 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -265,6 +265,7 @@ static int get_npt_level(struct kvm_vcpu *vcpu)
>   
>   void svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)
>   {
> +	struct vcpu_svm *svm = to_svm(vcpu);
>   	vcpu->arch.efer = efer;
>   
>   	if (!npt_enabled) {
> @@ -275,8 +276,13 @@ void svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)
>   			efer &= ~EFER_LME;
>   	}
>   
> -	to_svm(vcpu)->vmcb->save.efer = efer | EFER_SVME;
> -	mark_dirty(to_svm(vcpu)->vmcb, VMCB_CR);
> +	if (!(efer & EFER_SVME)) {
> +		svm_leave_nested(svm);
> +		svm_set_gif(svm, true);
> +	}
> +
> +	svm->vmcb->save.efer = efer | EFER_SVME;
> +	mark_dirty(svm->vmcb, VMCB_CR);
>   }
>   
>   static int is_external_interrupt(u32 info)
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index be8e830f83fa..6ac4c00a5d82 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -389,6 +389,7 @@ static inline bool nested_exit_on_nmi(struct vcpu_svm *svm)
>   
>   void enter_svm_guest_mode(struct vcpu_svm *svm, u64 vmcb_gpa,
>   			  struct vmcb *nested_vmcb);
> +void svm_leave_nested(struct vcpu_svm *svm);
>   int nested_svm_vmrun(struct vcpu_svm *svm);
>   void nested_svm_vmloadsave(struct vmcb *from_vmcb, struct vmcb *to_vmcb);
>   int nested_svm_vmexit(struct vcpu_svm *svm);
Paolo Bonzini June 1, 2020, 7:28 a.m. UTC | #2
On 01/06/20 04:26, Krish Sadhukhan wrote:
> On 5/29/20 8:39 AM, Paolo Bonzini wrote:
>> According to the AMD manual, the effect of turning off EFER.SVME while a
>> guest is running is undefined.  We make it leave guest mode immediately,
>> similar to the effect of clearing the VMX bit in MSR_IA32_FEAT_CTL.
> 
> I see that svm_set_efer() is called in enter_svm_guest_mode() and
> nested_svm_vmexit(). In the VMRUN path, we have already checked
> EFER.SVME in nested_vmcb_checks(). So if it was not set, we wouldn't
> come to enter_svm_guest_mode(). Your fix is only for the #VMEXIT path
> then ?

No, it's for KVM_SET_MSR.

Paolo

Patch
diff mbox series

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index bd3a89cd4070..369eca73fe3e 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -618,6 +618,22 @@  int nested_svm_vmexit(struct vcpu_svm *svm)
 	return 0;
 }
 
+/*
+ * Forcibly leave nested mode in order to be able to reset the VCPU later on.
+ */
+void svm_leave_nested(struct vcpu_svm *svm)
+{
+	if (is_guest_mode(&svm->vcpu)) {
+		struct vmcb *hsave = svm->nested.hsave;
+		struct vmcb *vmcb = svm->vmcb;
+
+		svm->nested.nested_run_pending = 0;
+		leave_guest_mode(&svm->vcpu);
+		copy_vmcb_control_area(&vmcb->control, &hsave->control);
+		nested_svm_uninit_mmu_context(&svm->vcpu);
+	}
+}
+
 static int nested_svm_exit_handled_msr(struct vcpu_svm *svm)
 {
 	u32 offset, msr, value;
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index bc08221f6743..b4db9a980469 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -265,6 +265,7 @@  static int get_npt_level(struct kvm_vcpu *vcpu)
 
 void svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)
 {
+	struct vcpu_svm *svm = to_svm(vcpu);
 	vcpu->arch.efer = efer;
 
 	if (!npt_enabled) {
@@ -275,8 +276,13 @@  void svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)
 			efer &= ~EFER_LME;
 	}
 
-	to_svm(vcpu)->vmcb->save.efer = efer | EFER_SVME;
-	mark_dirty(to_svm(vcpu)->vmcb, VMCB_CR);
+	if (!(efer & EFER_SVME)) {
+		svm_leave_nested(svm);
+		svm_set_gif(svm, true);
+	}
+
+	svm->vmcb->save.efer = efer | EFER_SVME;
+	mark_dirty(svm->vmcb, VMCB_CR);
 }
 
 static int is_external_interrupt(u32 info)
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index be8e830f83fa..6ac4c00a5d82 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -389,6 +389,7 @@  static inline bool nested_exit_on_nmi(struct vcpu_svm *svm)
 
 void enter_svm_guest_mode(struct vcpu_svm *svm, u64 vmcb_gpa,
 			  struct vmcb *nested_vmcb);
+void svm_leave_nested(struct vcpu_svm *svm);
 int nested_svm_vmrun(struct vcpu_svm *svm);
 void nested_svm_vmloadsave(struct vmcb *from_vmcb, struct vmcb *to_vmcb);
 int nested_svm_vmexit(struct vcpu_svm *svm);