2022-02-21 03:43:02

by Suthikulpanit, Suravee

Subject: [RFC PATCH 12/13] KVM: SVM: Remove APICv inhibit reasone due to x2APIC

Currently, AVIC is inactive when booting a VM w/ x2APIC support.
With x2AVIC support, the APICV_INHIBIT_REASON_X2APIC can be removed.

Signed-off-by: Suravee Suthikulpanit <[email protected]>
---
arch/x86/kvm/svm/avic.c | 21 +++++++++++++++++++++
arch/x86/kvm/svm/svm.c | 18 ++----------------
arch/x86/kvm/svm/svm.h | 1 +
3 files changed, 24 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 3306b74f1d8b..874c89f8fd47 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -21,6 +21,7 @@

#include <asm/irq_remapping.h>

+#include "cpuid.h"
#include "trace.h"
#include "lapic.h"
#include "x86.h"
@@ -176,6 +177,26 @@ void avic_vm_destroy(struct kvm *kvm)
spin_unlock_irqrestore(&svm_vm_data_hash_lock, flags);
}

+void avic_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu, int nested)
+{
+ /*
+ * If the X2APIC feature is exposed to the guest,
+ * disable AVIC unless X2AVIC mode is enabled.
+ */
+ if (avic_mode == AVIC_MODE_X1 &&
+ guest_cpuid_has(vcpu, X86_FEATURE_X2APIC))
+ kvm_request_apicv_update(vcpu->kvm, false,
+ APICV_INHIBIT_REASON_X2APIC);
+
+ /*
+ * Currently, AVIC does not work with nested virtualization.
+ * So, we disable AVIC when cpuid for SVM is set in the L1 guest.
+ */
+ if (nested && guest_cpuid_has(vcpu, X86_FEATURE_SVM))
+ kvm_request_apicv_update(vcpu->kvm, false,
+ APICV_INHIBIT_REASON_NESTED);
+}
+
int avic_vm_init(struct kvm *kvm)
{
unsigned long flags;
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index afca26aa1f40..b7bc6cd74aba 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3992,23 +3992,9 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
vcpu->arch.reserved_gpa_bits &= ~(1UL << (best->ebx & 0x3f));
}

- if (kvm_vcpu_apicv_active(vcpu)) {
- /*
- * AVIC does not work with an x2APIC mode guest. If the X2APIC feature
- * is exposed to the guest, disable AVIC.
- */
- if (guest_cpuid_has(vcpu, X86_FEATURE_X2APIC))
- kvm_request_apicv_update(vcpu->kvm, false,
- APICV_INHIBIT_REASON_X2APIC);
+ if (kvm_vcpu_apicv_active(vcpu))
+ avic_vcpu_after_set_cpuid(vcpu, nested);

- /*
- * Currently, AVIC does not work with nested virtualization.
- * So, we disable AVIC when cpuid for SVM is set in the L1 guest.
- */
- if (nested && guest_cpuid_has(vcpu, X86_FEATURE_SVM))
- kvm_request_apicv_update(vcpu->kvm, false,
- APICV_INHIBIT_REASON_NESTED);
- }
init_vmcb_after_set_cpuid(vcpu);
}

diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 41514df5107e..aea80abe9186 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -578,6 +578,7 @@ void avic_update_vapic_bar(struct vcpu_svm *svm, u64 data);
void avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu);
void avic_vcpu_put(struct kvm_vcpu *vcpu);
void avic_post_state_restore(struct kvm_vcpu *vcpu);
+void avic_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu, int nested);
void svm_set_virtual_apic_mode(struct kvm_vcpu *vcpu);
void svm_refresh_apicv_exec_ctrl(struct kvm_vcpu *vcpu);
bool svm_check_apicv_inhibit_reasons(ulong bit);
--
2.25.1

2022-02-24 21:28:48

by Maxim Levitsky

Subject: Re: [RFC PATCH 12/13] KVM: SVM: Remove APICv inhibit reasone due to x2APIC

On Sun, 2022-02-20 at 20:19 -0600, Suravee Suthikulpanit wrote:
> Currently, AVIC is inactive when booting a VM w/ x2APIC support.
> With x2AVIC support, the APICV_INHIBIT_REASON_X2APIC can be removed.
The commit title is a bit misleading - the inhibit reason is not removed,
but rather AVIC is not inhibited when x2avic is present.

>
> Signed-off-by: Suravee Suthikulpanit <[email protected]>
> ---
> arch/x86/kvm/svm/avic.c | 21 +++++++++++++++++++++
> arch/x86/kvm/svm/svm.c | 18 ++----------------
> arch/x86/kvm/svm/svm.h | 1 +
> 3 files changed, 24 insertions(+), 16 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> index 3306b74f1d8b..874c89f8fd47 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -21,6 +21,7 @@
>
> #include <asm/irq_remapping.h>
>
> +#include "cpuid.h"
> #include "trace.h"
> #include "lapic.h"
> #include "x86.h"
> @@ -176,6 +177,26 @@ void avic_vm_destroy(struct kvm *kvm)
> spin_unlock_irqrestore(&svm_vm_data_hash_lock, flags);
> }
>
> +void avic_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu, int nested)
> +{
> + /*
> + * If the X2APIC feature is exposed to the guest,
> + * disable AVIC unless X2AVIC mode is enabled.
> + */
> + if (avic_mode == AVIC_MODE_X1 &&
> + guest_cpuid_has(vcpu, X86_FEATURE_X2APIC))
> + kvm_request_apicv_update(vcpu->kvm, false,
> + APICV_INHIBIT_REASON_X2APIC);
> +
> + /*
> + * Currently, AVIC does not work with nested virtualization.
> + * So, we disable AVIC when cpuid for SVM is set in the L1 guest.
> + */
> + if (nested && guest_cpuid_has(vcpu, X86_FEATURE_SVM))
> + kvm_request_apicv_update(vcpu->kvm, false,
> + APICV_INHIBIT_REASON_NESTED);

BTW, now that I am thinking about it, it would be nice to be able to force
the AVIC_MODE_X1 even if x2avic is present, for debug purposes from a module
param. Just a suggestion.

> +}
> +
> int avic_vm_init(struct kvm *kvm)
> {
> unsigned long flags;
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index afca26aa1f40..b7bc6cd74aba 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -3992,23 +3992,9 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
> vcpu->arch.reserved_gpa_bits &= ~(1UL << (best->ebx & 0x3f));
> }
>
> - if (kvm_vcpu_apicv_active(vcpu)) {
> - /*
> - * AVIC does not work with an x2APIC mode guest. If the X2APIC feature
> - * is exposed to the guest, disable AVIC.
> - */
> - if (guest_cpuid_has(vcpu, X86_FEATURE_X2APIC))
> - kvm_request_apicv_update(vcpu->kvm, false,
> - APICV_INHIBIT_REASON_X2APIC);
> + if (kvm_vcpu_apicv_active(vcpu))
> + avic_vcpu_after_set_cpuid(vcpu, nested);
>
> - /*
> - * Currently, AVIC does not work with nested virtualization.
> - * So, we disable AVIC when cpuid for SVM is set in the L1 guest.
> - */
> - if (nested && guest_cpuid_has(vcpu, X86_FEATURE_SVM))
> - kvm_request_apicv_update(vcpu->kvm, false,
> - APICV_INHIBIT_REASON_NESTED);
> - }
> init_vmcb_after_set_cpuid(vcpu);
> }
>
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 41514df5107e..aea80abe9186 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -578,6 +578,7 @@ void avic_update_vapic_bar(struct vcpu_svm *svm, u64 data);
> void avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu);
> void avic_vcpu_put(struct kvm_vcpu *vcpu);
> void avic_post_state_restore(struct kvm_vcpu *vcpu);
> +void avic_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu, int nested);
> void svm_set_virtual_apic_mode(struct kvm_vcpu *vcpu);
> void svm_refresh_apicv_exec_ctrl(struct kvm_vcpu *vcpu);
> bool svm_check_apicv_inhibit_reasons(ulong bit);

Reviewed-by: Maxim Levitsky <[email protected]>

Best regards,
Maxim Levitsky

2022-03-01 15:25:00

by Suthikulpanit, Suravee

Subject: Re: [RFC PATCH 12/13] KVM: SVM: Remove APICv inhibit reasone due to x2APIC

Hi Maxim,

On 2/25/22 3:06 AM, Maxim Levitsky wrote:
> On Sun, 2022-02-20 at 20:19 -0600, Suravee Suthikulpanit wrote:
>> Currently, AVIC is inactive when booting a VM w/ x2APIC support.
>> With x2AVIC support, the APICV_INHIBIT_REASON_X2APIC can be removed.
> The commit title is a bit misleading - the inhibit reason is not removed,
> but rather AVIC is not inhibited when x2avic is present.
>

I'll fix the commit message.

>> Signed-off-by: Suravee Suthikulpanit<[email protected]>
>> ---
>> arch/x86/kvm/svm/avic.c | 21 +++++++++++++++++++++
>> arch/x86/kvm/svm/svm.c | 18 ++----------------
>> arch/x86/kvm/svm/svm.h | 1 +
>> 3 files changed, 24 insertions(+), 16 deletions(-)
>>
>> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
>> index 3306b74f1d8b..874c89f8fd47 100644
>> --- a/arch/x86/kvm/svm/avic.c
>> +++ b/arch/x86/kvm/svm/avic.c
>> @@ -21,6 +21,7 @@
>>
>> #include <asm/irq_remapping.h>
>>
>> +#include "cpuid.h"
>> #include "trace.h"
>> #include "lapic.h"
>> #include "x86.h"
>> @@ -176,6 +177,26 @@ void avic_vm_destroy(struct kvm *kvm)
>> spin_unlock_irqrestore(&svm_vm_data_hash_lock, flags);
>> }
>>
>> +void avic_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu, int nested)
>> +{
>> + /*
>> + * If the X2APIC feature is exposed to the guest,
>> + * disable AVIC unless X2AVIC mode is enabled.
>> + */
>> + if (avic_mode == AVIC_MODE_X1 &&
>> + guest_cpuid_has(vcpu, X86_FEATURE_X2APIC))
>> + kvm_request_apicv_update(vcpu->kvm, false,
>> + APICV_INHIBIT_REASON_X2APIC);
>> +
>> + /*
>> + * Currently, AVIC does not work with nested virtualization.
>> + * So, we disable AVIC when cpuid for SVM is set in the L1 guest.
>> + */
>> + if (nested && guest_cpuid_has(vcpu, X86_FEATURE_SVM))
>> + kvm_request_apicv_update(vcpu->kvm, false,
>> + APICV_INHIBIT_REASON_NESTED);
> BTW, now that I am thinking about it, it would be nice to be able to force
> the AVIC_MODE_X1 even if x2avic is present, for debug purposes from a module
> param. Just a suggestion.

Actually, we can force AVIC_MODE_X1 on a VM by disabling Guest x2APIC mode via QEMU option.
That should work for debugging purpose, right?

Regards,
Suravee