[PATCH] svm: Fix improper check when deactivate AVIC

[PATCH] svm: Fix improper check when deactivate AVIC

[Suthikulpanit, Suravee]

The function svm_refresh_apicv_exec_ctrl() always returning prematurely
as kvm_vcpu_apicv_active() always return false when calling from
the function arch/x86/kvm/x86.c:kvm_vcpu_deactivate_apicv().
This is because the apicv_active is set to false just before calling
refresh_apicv_exec_ctrl().

Also, we need to mark VMCB_AVIC bit as dirty instead of VMCB_INTR.

So, fix svm_refresh_apicv_exec_ctrl() to properly deactivate AVIC.

Fixes: 67034bb9dd5e ('KVM: SVM: Add irqchip_split() checks before enabling AVIC')
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
---
 arch/x86/kvm/svm.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index d35c9002f282..59b1f68060c7 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -390,6 +390,8 @@ static int nested_svm_vmexit(struct vcpu_svm *svm);
 static int nested_svm_check_exception(struct vcpu_svm *svm, unsigned nr,
 				      bool has_error_code, u32 error_code);
 
+static bool svm_get_enable_apicv(struct kvm_vcpu *vcpu);
+
 enum {
 	VMCB_INTERCEPTS, /* Intercept vectors, TSC offset,
 			    pause filter count */
@@ -478,6 +480,12 @@ static inline struct vcpu_svm *to_svm(struct kvm_vcpu *vcpu)
 	return container_of(vcpu, struct vcpu_svm, vcpu);
 }
 
+static bool is_avic_active(struct vcpu_svm *svm)
+{
+	return (svm_get_enable_apicv(&svm->vcpu) &&
+		svm->vmcb->control.int_ctl & AVIC_ENABLE_MASK);
+}
+
 static inline void avic_update_vapic_bar(struct vcpu_svm *svm, u64 data)
 {
 	svm->vmcb->control.avic_vapic_bar = data & VMCB_AVIC_APIC_BAR_MASK;
@@ -5108,17 +5116,23 @@ static void svm_hwapic_isr_update(struct kvm_vcpu *vcpu, int max_isr)
 {
 }
 
-/* Note: Currently only used by Hyper-V. */
-static void svm_refresh_apicv_exec_ctrl(struct kvm_vcpu *vcpu)
+static void svm_deactivate_avic(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 	struct vmcb *vmcb = svm->vmcb;
 
-	if (!kvm_vcpu_apicv_active(&svm->vcpu))
+	if (!lapic_in_kernel(vcpu) || !is_avic_active(svm))
 		return;
 
 	vmcb->control.int_ctl &= ~AVIC_ENABLE_MASK;
-	mark_dirty(vmcb, VMCB_INTR);
+	mark_dirty(vmcb, VMCB_AVIC);
+}
+
+/* Note: Currently only used by Hyper-V. */
+static void svm_refresh_apicv_exec_ctrl(struct kvm_vcpu *vcpu)
+{
+	if (!kvm_vcpu_apicv_active(vcpu))
+		svm_deactivate_avic(vcpu);
 }
 
 static void svm_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap)
-- 
2.17.1

Re: [PATCH] svm: Fix improper check when deactivate AVIC

[Paolo Bonzini]

On 29/01/19 09:09, Suthikulpanit, Suravee wrote:
> The function svm_refresh_apicv_exec_ctrl() always returning prematurely
> as kvm_vcpu_apicv_active() always return false when calling from
> the function arch/x86/kvm/x86.c:kvm_vcpu_deactivate_apicv().
> This is because the apicv_active is set to false just before calling
> refresh_apicv_exec_ctrl().
> 
> Also, we need to mark VMCB_AVIC bit as dirty instead of VMCB_INTR.
> 
> So, fix svm_refresh_apicv_exec_ctrl() to properly deactivate AVIC.
> 
> Fixes: 67034bb9dd5e ('KVM: SVM: Add irqchip_split() checks before enabling AVIC')

Having the lapic_in_kernel check in your code is a bit ugly - the caller
should check it.  And actually, even though it doesn't check it right
now, svm_refresh_apicv_exec_ctrl is only reachable if lapic_in_kernel
returns true; see the KVM_CAP_HYPERV_SYNIC case of
kvm_vcpu_ioctl_enable_cap.

What about this simpler patch:

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 01b66bbcdd7a..74ceda470eae 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -5122,11 +5122,11 @@ static void svm_refresh_apicv_exec_ctrl(
 	struct vcpu_svm *svm = to_svm(vcpu);
 	struct vmcb *vmcb = svm->vmcb;

-	if (!kvm_vcpu_apicv_active(&svm->vcpu))
-		return;
-
-	vmcb->control.int_ctl &= ~AVIC_ENABLE_MASK;
-	mark_dirty(vmcb, VMCB_INTR);
+	if (kvm_vcpu_apicv_active(vcpu))
+		vmcb->control.int_ctl |= AVIC_ENABLE_MASK;
+	else
+		vmcb->control.int_ctl &= ~AVIC_ENABLE_MASK;
+	mark_dirty(vmcb, VMCB_AVIC);
 }

 static void svm_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64
*eoi_exit_bitmap)

?

Thanks,

Paolo

Re: [PATCH] svm: Fix improper check when deactivate AVIC

[Suthikulpanit, Suravee]

Paolo,

On 1/30/19 11:22 PM, Paolo Bonzini wrote:
> On 29/01/19 09:09, Suthikulpanit, Suravee wrote:
>> The function svm_refresh_apicv_exec_ctrl() always returning prematurely
>> as kvm_vcpu_apicv_active() always return false when calling from
>> the function arch/x86/kvm/x86.c:kvm_vcpu_deactivate_apicv().
>> This is because the apicv_active is set to false just before calling
>> refresh_apicv_exec_ctrl().
>>
>> Also, we need to mark VMCB_AVIC bit as dirty instead of VMCB_INTR.
>>
>> So, fix svm_refresh_apicv_exec_ctrl() to properly deactivate AVIC.
>>
>> Fixes: 67034bb9dd5e ('KVM: SVM: Add irqchip_split() checks before enabling AVIC')
> 
> Having the lapic_in_kernel check in your code is a bit ugly - the caller
> should check it.  And actually, even though it doesn't check it right
> now, svm_refresh_apicv_exec_ctrl is only reachable if lapic_in_kernel
> returns true; see the KVM_CAP_HYPERV_SYNIC case of
> kvm_vcpu_ioctl_enable_cap.
> 
> What about this simpler patch:
> 
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 01b66bbcdd7a..74ceda470eae 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -5122,11 +5122,11 @@ static void svm_refresh_apicv_exec_ctrl(
>   	struct vcpu_svm *svm = to_svm(vcpu);
>   	struct vmcb *vmcb = svm->vmcb;
> 
> -	if (!kvm_vcpu_apicv_active(&svm->vcpu))
> -		return;
> -
> -	vmcb->control.int_ctl &= ~AVIC_ENABLE_MASK;
> -	mark_dirty(vmcb, VMCB_INTR);
> +	if (kvm_vcpu_apicv_active(vcpu))
> +		vmcb->control.int_ctl |= AVIC_ENABLE_MASK;
> +	else
> +		vmcb->control.int_ctl &= ~AVIC_ENABLE_MASK;
> +	mark_dirty(vmcb, VMCB_AVIC);
>   }
> 
>   static void svm_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64
> *eoi_exit_bitmap)
> 
> ?
> 
> Thanks,
> 
> Paolo
> 

Yes, this would work.

This patch is actually a precursor of a patch series that I am working on
to allow AVIC enabling/disabling during run-time. I will send out a series
for RFC soon.

Thanks,
Suravee

Re: [PATCH] svm: Fix improper check when deactivate AVIC

[Suthikulpanit, Suravee]

Paolo,

On 2/1/19 6:01 PM, Suravee Suthikulpanit wrote:
> Paolo,
> 
> On 1/30/19 11:22 PM, Paolo Bonzini wrote:
>> On 29/01/19 09:09, Suthikulpanit, Suravee wrote:
>>> The function svm_refresh_apicv_exec_ctrl() always returning prematurely
>>> as kvm_vcpu_apicv_active() always return false when calling from
>>> the function arch/x86/kvm/x86.c:kvm_vcpu_deactivate_apicv().
>>> This is because the apicv_active is set to false just before calling
>>> refresh_apicv_exec_ctrl().
>>>
>>> Also, we need to mark VMCB_AVIC bit as dirty instead of VMCB_INTR.
>>>
>>> So, fix svm_refresh_apicv_exec_ctrl() to properly deactivate AVIC.
>>>
>>> Fixes: 67034bb9dd5e ('KVM: SVM: Add irqchip_split() checks before enabling AVIC')
>>
>> Having the lapic_in_kernel check in your code is a bit ugly - the caller
>> should check it.  And actually, even though it doesn't check it right
>> now, svm_refresh_apicv_exec_ctrl is only reachable if lapic_in_kernel
>> returns true; see the KVM_CAP_HYPERV_SYNIC case of
>> kvm_vcpu_ioctl_enable_cap.
>>
>> What about this simpler patch:
>>
>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>> index 01b66bbcdd7a..74ceda470eae 100644
>> --- a/arch/x86/kvm/svm.c
>> +++ b/arch/x86/kvm/svm.c
>> @@ -5122,11 +5122,11 @@ static void svm_refresh_apicv_exec_ctrl(
>>       struct vcpu_svm *svm = to_svm(vcpu);
>>       struct vmcb *vmcb = svm->vmcb;
>>
>> -    if (!kvm_vcpu_apicv_active(&svm->vcpu))
>> -        return;
>> -
>> -    vmcb->control.int_ctl &= ~AVIC_ENABLE_MASK;
>> -    mark_dirty(vmcb, VMCB_INTR);
>> +    if (kvm_vcpu_apicv_active(vcpu))
>> +        vmcb->control.int_ctl |= AVIC_ENABLE_MASK;
>> +    else
>> +        vmcb->control.int_ctl &= ~AVIC_ENABLE_MASK;
>> +    mark_dirty(vmcb, VMCB_AVIC);
>>   }
>>
>>   static void svm_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64
>> *eoi_exit_bitmap)
>>
>> ?
>>
>> Thanks,
>>
>> Paolo
>>
> 
> Yes, this would work.
> 
> This patch is actually a precursor of a patch series that I am working on
> to allow AVIC enabling/disabling during run-time. I will send out a series
> for RFC soon.
> 
> Thanks,
> Suravee

Not sure if you have already applied this change. Anyhow, I just want to let
you know that I have included the change you suggested as patch 1/8 of
the RFC series

"KVM: x86: svm: Enabling AVIC with in kernel irqchip"

Thanks,
Suravee