2021-11-30 12:38:17

by Paolo Bonzini

Subject: [PATCH] KVM: ensure APICv is considered inactive if there is no APIC

kvm_vcpu_apicv_active() returns false if a virtual machine has no in-kernel
local APIC, however kvm_apicv_activated might still be true if there are
no reasons to disable APICv; in fact it is quite likely that there is none
because APICv is inhibited by specific configurations of the local APIC
and those configurations cannot be programmed. This triggers a WARN:

WARN_ON_ONCE(kvm_apicv_activated(vcpu->kvm) != kvm_vcpu_apicv_active(vcpu));

To avoid this, introduce another cause for APICv inhibition, namely the
absence of an in-kernel local APIC. This cause is enabled by default,
and is dropped by either KVM_CREATE_IRQCHIP or the enabling of
KVM_CAP_IRQCHIP_SPLIT.

Reported-by: Ignat Korchagin <[email protected]>
Fixes: ee49a8932971 ("KVM: x86: Move SVM's APICv sanity check to common x86", 2021-10-22)
Signed-off-by: Paolo Bonzini <[email protected]>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/svm/avic.c | 1 +
arch/x86/kvm/vmx/vmx.c | 1 +
arch/x86/kvm/x86.c | 9 +++++----
4 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 6ac61f85e07b..860ed500580c 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1036,6 +1036,7 @@ struct kvm_x86_msr_filter {
#define APICV_INHIBIT_REASON_PIT_REINJ 4
#define APICV_INHIBIT_REASON_X2APIC 5
#define APICV_INHIBIT_REASON_BLOCKIRQ 6
+#define APICV_INHIBIT_REASON_ABSENT 7

struct kvm_arch {
unsigned long n_used_mmu_pages;
diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index affc0ea98d30..5a55a78e2f50 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -900,6 +900,7 @@ int svm_update_pi_irte(struct kvm *kvm, unsigned int host_irq,
bool svm_check_apicv_inhibit_reasons(ulong bit)
{
ulong supported = BIT(APICV_INHIBIT_REASON_DISABLE) |
+ BIT(APICV_INHIBIT_REASON_ABSENT) |
BIT(APICV_INHIBIT_REASON_HYPERV) |
BIT(APICV_INHIBIT_REASON_NESTED) |
BIT(APICV_INHIBIT_REASON_IRQWIN) |
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 1fadec8cbf96..ca1fd93c1dc9 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7525,6 +7525,7 @@ static void hardware_unsetup(void)
static bool vmx_check_apicv_inhibit_reasons(ulong bit)
{
ulong supported = BIT(APICV_INHIBIT_REASON_DISABLE) |
+ BIT(APICV_INHIBIT_REASON_ABSENT) |
BIT(APICV_INHIBIT_REASON_HYPERV) |
BIT(APICV_INHIBIT_REASON_BLOCKIRQ);

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0ee1a039b490..e0aa4dd53c7f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5740,6 +5740,7 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
smp_wmb();
kvm->arch.irqchip_mode = KVM_IRQCHIP_SPLIT;
kvm->arch.nr_reserved_ioapic_pins = cap->args[0];
+ kvm_request_apicv_update(kvm, true, APICV_INHIBIT_REASON_ABSENT);
r = 0;
split_irqchip_unlock:
mutex_unlock(&kvm->lock);
@@ -6120,6 +6121,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
/* Write kvm->irq_routing before enabling irqchip_in_kernel. */
smp_wmb();
kvm->arch.irqchip_mode = KVM_IRQCHIP_KERNEL;
+ kvm_request_apicv_update(kvm, true, APICV_INHIBIT_REASON_ABSENT);
create_irqchip_unlock:
mutex_unlock(&kvm->lock);
break;
@@ -8818,10 +8820,9 @@ static void kvm_apicv_init(struct kvm *kvm)
{
init_rwsem(&kvm->arch.apicv_update_lock);

- if (enable_apicv)
- clear_bit(APICV_INHIBIT_REASON_DISABLE,
- &kvm->arch.apicv_inhibit_reasons);
- else
+ set_bit(APICV_INHIBIT_REASON_ABSENT,
+ &kvm->arch.apicv_inhibit_reasons);
+ if (!enable_apicv)
set_bit(APICV_INHIBIT_REASON_DISABLE,
&kvm->arch.apicv_inhibit_reasons);
}
--
2.31.1

2021-11-30 13:06:14

by Ignat Korchagin

Subject: Re: [PATCH] KVM: ensure APICv is considered inactive if there is no APIC

On Tue, Nov 30, 2021 at 12:37 PM Paolo Bonzini <[email protected]> wrote:
>
> kvm_vcpu_apicv_active() returns false if a virtual machine has no in-kernel
> local APIC, however kvm_apicv_activated might still be true if there are
> no reasons to disable APICv; in fact it is quite likely that there is none
> because APICv is inhibited by specific configurations of the local APIC
> and those configurations cannot be programmed. This triggers a WARN:
>
> WARN_ON_ONCE(kvm_apicv_activated(vcpu->kvm) != kvm_vcpu_apicv_active(vcpu));
>
> To avoid this, introduce another cause for APICv inhibition, namely the
> absence of an in-kernel local APIC. This cause is enabled by default,
> and is dropped by either KVM_CREATE_IRQCHIP or the enabling of
> KVM_CAP_IRQCHIP_SPLIT.
>
> Reported-by: Ignat Korchagin <[email protected]>
> Fixes: ee49a8932971 ("KVM: x86: Move SVM's APICv sanity check to common x86", 2021-10-22)
> Signed-off-by: Paolo Bonzini <[email protected]>
> ---
> arch/x86/include/asm/kvm_host.h | 1 +
> arch/x86/kvm/svm/avic.c | 1 +
> arch/x86/kvm/vmx/vmx.c | 1 +
> arch/x86/kvm/x86.c | 9 +++++----
> 4 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 6ac61f85e07b..860ed500580c 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1036,6 +1036,7 @@ struct kvm_x86_msr_filter {
> #define APICV_INHIBIT_REASON_PIT_REINJ 4
> #define APICV_INHIBIT_REASON_X2APIC 5
> #define APICV_INHIBIT_REASON_BLOCKIRQ 6
> +#define APICV_INHIBIT_REASON_ABSENT 7
>
> struct kvm_arch {
> unsigned long n_used_mmu_pages;
> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> index affc0ea98d30..5a55a78e2f50 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -900,6 +900,7 @@ int svm_update_pi_irte(struct kvm *kvm, unsigned int host_irq,
> bool svm_check_apicv_inhibit_reasons(ulong bit)
> {
> ulong supported = BIT(APICV_INHIBIT_REASON_DISABLE) |
> + BIT(APICV_INHIBIT_REASON_ABSENT) |
> BIT(APICV_INHIBIT_REASON_HYPERV) |
> BIT(APICV_INHIBIT_REASON_NESTED) |
> BIT(APICV_INHIBIT_REASON_IRQWIN) |
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 1fadec8cbf96..ca1fd93c1dc9 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7525,6 +7525,7 @@ static void hardware_unsetup(void)
> static bool vmx_check_apicv_inhibit_reasons(ulong bit)
> {
> ulong supported = BIT(APICV_INHIBIT_REASON_DISABLE) |
> + BIT(APICV_INHIBIT_REASON_ABSENT) |
> BIT(APICV_INHIBIT_REASON_HYPERV) |
> BIT(APICV_INHIBIT_REASON_BLOCKIRQ);
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 0ee1a039b490..e0aa4dd53c7f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5740,6 +5740,7 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
> smp_wmb();
> kvm->arch.irqchip_mode = KVM_IRQCHIP_SPLIT;
> kvm->arch.nr_reserved_ioapic_pins = cap->args[0];
> + kvm_request_apicv_update(kvm, true, APICV_INHIBIT_REASON_ABSENT);
> r = 0;
> split_irqchip_unlock:
> mutex_unlock(&kvm->lock);
> @@ -6120,6 +6121,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
> /* Write kvm->irq_routing before enabling irqchip_in_kernel. */
> smp_wmb();
> kvm->arch.irqchip_mode = KVM_IRQCHIP_KERNEL;
> + kvm_request_apicv_update(kvm, true, APICV_INHIBIT_REASON_ABSENT);
> create_irqchip_unlock:
> mutex_unlock(&kvm->lock);
> break;
> @@ -8818,10 +8820,9 @@ static void kvm_apicv_init(struct kvm *kvm)
> {
> init_rwsem(&kvm->arch.apicv_update_lock);
>
> - if (enable_apicv)
> - clear_bit(APICV_INHIBIT_REASON_DISABLE,
> - &kvm->arch.apicv_inhibit_reasons);
> - else
> + set_bit(APICV_INHIBIT_REASON_ABSENT,
> + &kvm->arch.apicv_inhibit_reasons);
> + if (!enable_apicv)
> set_bit(APICV_INHIBIT_REASON_DISABLE,
> &kvm->arch.apicv_inhibit_reasons);
> }
> --
> 2.31.1
>

Tested-by: Ignat Korchagin <[email protected]>

2021-11-30 20:39:30

by Sean Christopherson

Subject: Re: [PATCH] KVM: ensure APICv is considered inactive if there is no APIC

On Tue, Nov 30, 2021, Paolo Bonzini wrote:
> kvm_vcpu_apicv_active() returns false if a virtual machine has no in-kernel
> local APIC, however kvm_apicv_activated might still be true if there are
> no reasons to disable APICv; in fact it is quite likely that there is none
> because APICv is inhibited by specific configurations of the local APIC
> and those configurations cannot be programmed. This triggers a WARN:
>
> WARN_ON_ONCE(kvm_apicv_activated(vcpu->kvm) != kvm_vcpu_apicv_active(vcpu));
>
> To avoid this, introduce another cause for APICv inhibition, namely the
> absence of an in-kernel local APIC. This cause is enabled by default,
> and is dropped by either KVM_CREATE_IRQCHIP or the enabling of
> KVM_CAP_IRQCHIP_SPLIT.
>
> Reported-by: Ignat Korchagin <[email protected]>
> Fixes: ee49a8932971 ("KVM: x86: Move SVM's APICv sanity check to common x86", 2021-10-22)
> Signed-off-by: Paolo Bonzini <[email protected]>
> ---

Reviewed-by: Sean Christopherson <[email protected]>

> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 0ee1a039b490..e0aa4dd53c7f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5740,6 +5740,7 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
> smp_wmb();
> kvm->arch.irqchip_mode = KVM_IRQCHIP_SPLIT;
> kvm->arch.nr_reserved_ioapic_pins = cap->args[0];
> + kvm_request_apicv_update(kvm, true, APICV_INHIBIT_REASON_ABSENT);
> r = 0;
> split_irqchip_unlock:
> mutex_unlock(&kvm->lock);
> @@ -6120,6 +6121,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
> /* Write kvm->irq_routing before enabling irqchip_in_kernel. */
> smp_wmb();
> kvm->arch.irqchip_mode = KVM_IRQCHIP_KERNEL;
> + kvm_request_apicv_update(kvm, true, APICV_INHIBIT_REASON_ABSENT);

Blech, kvm_request_apicv_update() is very counter-intuitive, true == clear. :-/
Wrappers along the lines of kvm_{set,clear}_apicv_inhibit() would help a lot, and
would likely avoid a handful of newlines as well. I'll send a patch on top of this,
unless you want to do it while pushing this one out.

> create_irqchip_unlock:
> mutex_unlock(&kvm->lock);
> break;
> @@ -8818,10 +8820,9 @@ static void kvm_apicv_init(struct kvm *kvm)
> {
> init_rwsem(&kvm->arch.apicv_update_lock);
>
> - if (enable_apicv)
> - clear_bit(APICV_INHIBIT_REASON_DISABLE,
> - &kvm->arch.apicv_inhibit_reasons);
> - else
> + set_bit(APICV_INHIBIT_REASON_ABSENT,
> + &kvm->arch.apicv_inhibit_reasons);

Nit, this one fits on a single line.

> + if (!enable_apicv)
> set_bit(APICV_INHIBIT_REASON_DISABLE,
> &kvm->arch.apicv_inhibit_reasons);
> }
> --
> 2.31.1
>

2021-11-30 21:09:03

by Maxim Levitsky

Subject: Re: [PATCH] KVM: ensure APICv is considered inactive if there is no APIC

On Tue, 2021-11-30 at 20:39 +0000, Sean Christopherson wrote:
> On Tue, Nov 30, 2021, Paolo Bonzini wrote:
> > kvm_vcpu_apicv_active() returns false if a virtual machine has no in-kernel
> > local APIC, however kvm_apicv_activated might still be true if there are
> > no reasons to disable APICv; in fact it is quite likely that there is none
> > because APICv is inhibited by specific configurations of the local APIC
> > and those configurations cannot be programmed. This triggers a WARN:
> >
> > WARN_ON_ONCE(kvm_apicv_activated(vcpu->kvm) != kvm_vcpu_apicv_active(vcpu));
> >
> > To avoid this, introduce another cause for APICv inhibition, namely the
> > absence of an in-kernel local APIC. This cause is enabled by default,
> > and is dropped by either KVM_CREATE_IRQCHIP or the enabling of
> > KVM_CAP_IRQCHIP_SPLIT.
> >
> > Reported-by: Ignat Korchagin <[email protected]>
> > Fixes: ee49a8932971 ("KVM: x86: Move SVM's APICv sanity check to common x86", 2021-10-22)
> > Signed-off-by: Paolo Bonzini <[email protected]>
> > ---
>
> Reviewed-by: Sean Christopherson <[email protected]>
>
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 0ee1a039b490..e0aa4dd53c7f 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -5740,6 +5740,7 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
> > smp_wmb();
> > kvm->arch.irqchip_mode = KVM_IRQCHIP_SPLIT;
> > kvm->arch.nr_reserved_ioapic_pins = cap->args[0];
> > + kvm_request_apicv_update(kvm, true, APICV_INHIBIT_REASON_ABSENT);
> > r = 0;
> > split_irqchip_unlock:
> > mutex_unlock(&kvm->lock);
> > @@ -6120,6 +6121,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
> > /* Write kvm->irq_routing before enabling irqchip_in_kernel. */
> > smp_wmb();
> > kvm->arch.irqchip_mode = KVM_IRQCHIP_KERNEL;
> > + kvm_request_apicv_update(kvm, true, APICV_INHIBIT_REASON_ABSENT);
>
> Blech, kvm_request_apicv_update() is very counter-intuitive, true == clear. :-/
> Wrappers along the lines of kvm_{set,clear}_apicv_inhibit() would help a lot, and
> would likely avoid a handful of newlines as well. I'll send a patch on top of this,
> unless you want to do it while pushing this one out.

100% agree that kvm_request_apicv_update() is very counter-intuitive!

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

Best regards,
Maxim Levitsky

>
> > create_irqchip_unlock:
> > mutex_unlock(&kvm->lock);
> > break;
> > @@ -8818,10 +8820,9 @@ static void kvm_apicv_init(struct kvm *kvm)
> > {
> > init_rwsem(&kvm->arch.apicv_update_lock);
> >
> > - if (enable_apicv)
> > - clear_bit(APICV_INHIBIT_REASON_DISABLE,
> > - &kvm->arch.apicv_inhibit_reasons);
> > - else
> > + set_bit(APICV_INHIBIT_REASON_ABSENT,
> > + &kvm->arch.apicv_inhibit_reasons);
>
> Nit, this one fits on a single line.
>
> > + if (!enable_apicv)
> > set_bit(APICV_INHIBIT_REASON_DISABLE,
> > &kvm->arch.apicv_inhibit_reasons);
> > }
> > --
> > 2.31.1
> >

2021-12-03 02:18:14

by Wanpeng Li

Subject: Re: [PATCH] KVM: ensure APICv is considered inactive if there is no APIC

On Wed, 1 Dec 2021 at 12:14, Paolo Bonzini <[email protected]> wrote:
>
> kvm_vcpu_apicv_active() returns false if a virtual machine has no in-kernel
> local APIC, however kvm_apicv_activated might still be true if there are
> no reasons to disable APICv; in fact it is quite likely that there is none
> because APICv is inhibited by specific configurations of the local APIC
> and those configurations cannot be programmed. This triggers a WARN:
>
> WARN_ON_ONCE(kvm_apicv_activated(vcpu->kvm) != kvm_vcpu_apicv_active(vcpu));
>
> To avoid this, introduce another cause for APICv inhibition, namely the
> absence of an in-kernel local APIC. This cause is enabled by default,
> and is dropped by either KVM_CREATE_IRQCHIP or the enabling of
> KVM_CAP_IRQCHIP_SPLIT.
>
> Reported-by: Ignat Korchagin <[email protected]>
> Fixes: ee49a8932971 ("KVM: x86: Move SVM's APICv sanity check to common x86", 2021-10-22)
> Signed-off-by: Paolo Bonzini <[email protected]>

Reviewed-by: Wanpeng Li <[email protected]>

> ---
> arch/x86/include/asm/kvm_host.h | 1 +
> arch/x86/kvm/svm/avic.c | 1 +
> arch/x86/kvm/vmx/vmx.c | 1 +
> arch/x86/kvm/x86.c | 9 +++++----
> 4 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 6ac61f85e07b..860ed500580c 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1036,6 +1036,7 @@ struct kvm_x86_msr_filter {
> #define APICV_INHIBIT_REASON_PIT_REINJ 4
> #define APICV_INHIBIT_REASON_X2APIC 5
> #define APICV_INHIBIT_REASON_BLOCKIRQ 6
> +#define APICV_INHIBIT_REASON_ABSENT 7
>
> struct kvm_arch {
> unsigned long n_used_mmu_pages;
> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> index affc0ea98d30..5a55a78e2f50 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -900,6 +900,7 @@ int svm_update_pi_irte(struct kvm *kvm, unsigned int host_irq,
> bool svm_check_apicv_inhibit_reasons(ulong bit)
> {
> ulong supported = BIT(APICV_INHIBIT_REASON_DISABLE) |
> + BIT(APICV_INHIBIT_REASON_ABSENT) |
> BIT(APICV_INHIBIT_REASON_HYPERV) |
> BIT(APICV_INHIBIT_REASON_NESTED) |
> BIT(APICV_INHIBIT_REASON_IRQWIN) |
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 1fadec8cbf96..ca1fd93c1dc9 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7525,6 +7525,7 @@ static void hardware_unsetup(void)
> static bool vmx_check_apicv_inhibit_reasons(ulong bit)
> {
> ulong supported = BIT(APICV_INHIBIT_REASON_DISABLE) |
> + BIT(APICV_INHIBIT_REASON_ABSENT) |
> BIT(APICV_INHIBIT_REASON_HYPERV) |
> BIT(APICV_INHIBIT_REASON_BLOCKIRQ);
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 0ee1a039b490..e0aa4dd53c7f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5740,6 +5740,7 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
> smp_wmb();
> kvm->arch.irqchip_mode = KVM_IRQCHIP_SPLIT;
> kvm->arch.nr_reserved_ioapic_pins = cap->args[0];
> + kvm_request_apicv_update(kvm, true, APICV_INHIBIT_REASON_ABSENT);
> r = 0;
> split_irqchip_unlock:
> mutex_unlock(&kvm->lock);
> @@ -6120,6 +6121,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
> /* Write kvm->irq_routing before enabling irqchip_in_kernel. */
> smp_wmb();
> kvm->arch.irqchip_mode = KVM_IRQCHIP_KERNEL;
> + kvm_request_apicv_update(kvm, true, APICV_INHIBIT_REASON_ABSENT);
> create_irqchip_unlock:
> mutex_unlock(&kvm->lock);
> break;
> @@ -8818,10 +8820,9 @@ static void kvm_apicv_init(struct kvm *kvm)
> {
> init_rwsem(&kvm->arch.apicv_update_lock);
>
> - if (enable_apicv)
> - clear_bit(APICV_INHIBIT_REASON_DISABLE,
> - &kvm->arch.apicv_inhibit_reasons);
> - else
> + set_bit(APICV_INHIBIT_REASON_ABSENT,
> + &kvm->arch.apicv_inhibit_reasons);
> + if (!enable_apicv)
> set_bit(APICV_INHIBIT_REASON_DISABLE,
> &kvm->arch.apicv_inhibit_reasons);
> }
> --
> 2.31.1
>