Re: [PATCH v4] KVM: x86: inhibit APICv when KVM_GUESTDBG_BLOCKIRQ active

[Paolo Bonzini]

On 11/8/21 10:02, Maxim Levitsky wrote:
> KVM_GUESTDBG_BLOCKIRQ relies on interrupts being injected using
> standard kvm's inject_pending_event, and not via APICv/AVIC.
>
> Since this is a debug feature, just inhibit APICv/AVIC while
> KVM_GUESTDBG_BLOCKIRQ is in use on at least one vCPU.
>
> Fixes: 61e5f69ef0837 ("KVM: x86: implement KVM_GUESTDBG_BLOCKIRQ")
>
> Reported-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> Reviewed-and-tested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>   arch/x86/include/asm/kvm_host.h |  1 +
>   arch/x86/kvm/svm/avic.c         |  3 ++-
>   arch/x86/kvm/vmx/vmx.c          |  3 ++-
>   arch/x86/kvm/x86.c              | 20 ++++++++++++++++++++
>   4 files changed, 25 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 88fce6ab4bbd7..8f6e15b95a4d8 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1034,6 +1034,7 @@ struct kvm_x86_msr_filter {
>   #define APICV_INHIBIT_REASON_IRQWIN     3
>   #define APICV_INHIBIT_REASON_PIT_REINJ  4
>   #define APICV_INHIBIT_REASON_X2APIC	5
> +#define APICV_INHIBIT_REASON_BLOCKIRQ	6
>   
>   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 8052d92069e01..affc0ea98d302 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -904,7 +904,8 @@ bool svm_check_apicv_inhibit_reasons(ulong bit)
>   			  BIT(APICV_INHIBIT_REASON_NESTED) |
>   			  BIT(APICV_INHIBIT_REASON_IRQWIN) |
>   			  BIT(APICV_INHIBIT_REASON_PIT_REINJ) |
> -			  BIT(APICV_INHIBIT_REASON_X2APIC);
> +			  BIT(APICV_INHIBIT_REASON_X2APIC) |
> +			  BIT(APICV_INHIBIT_REASON_BLOCKIRQ);
>   
>   	return supported & BIT(bit);
>   }
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 71f54d85f104c..e4fc9ff7cd944 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7565,7 +7565,8 @@ 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_HYPERV);
> +			  BIT(APICV_INHIBIT_REASON_HYPERV) |
> +			  BIT(APICV_INHIBIT_REASON_BLOCKIRQ);
>   
>   	return supported & BIT(bit);
>   }
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index ac83d873d65b0..6064ac47c8a37 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10703,6 +10703,24 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
>   	return ret;
>   }
>   
> +static void kvm_arch_vcpu_guestdbg_update_apicv_inhibit(struct kvm *kvm)
> +{
> +	bool inhibit = false;
> +	struct kvm_vcpu *vcpu;
> +	int i;
> +
> +	down_write(&kvm->arch.apicv_update_lock);
> +
> +	kvm_for_each_vcpu(i, vcpu, kvm) {
> +		if (vcpu->guest_debug & KVM_GUESTDBG_BLOCKIRQ) {
> +			inhibit = true;
> +			break;
> +		}
> +	}
> +	__kvm_request_apicv_update(kvm, !inhibit, APICV_INHIBIT_REASON_BLOCKIRQ);
> +	up_write(&kvm->arch.apicv_update_lock);
> +}
> +
>   int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
>   					struct kvm_guest_debug *dbg)
>   {
> @@ -10755,6 +10773,8 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
>   
>   	static_call(kvm_x86_update_exception_bitmap)(vcpu);
>   
> +	kvm_arch_vcpu_guestdbg_update_apicv_inhibit(vcpu->kvm);
> +
>   	r = 0;
>   
>   out:

Queued, thanks.

Paolo