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

Wanpeng Li
2021-12-03T02:18:14Z

On Wed, 1 Dec 2021 at 12:14, Paolo Bonzini <pbonzini@redhat.com> 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 <ignat@cloudflare.com>
> Fixes: ee49a8932971 ("KVM: x86: Move SVM's APICv sanity check to common x86", 2021-10-22)
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Reviewed-by: Wanpeng Li <wanpengli@tencent.com>

> ---
> 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);