Re: [PATCH v2] KVM: x86: inhibit APICv when KVM_GUESTDBG_BLOCKIRQ active

Vitaly Kuznetsov
2021-11-03T13:28:49Z

Maxim Levitsky <mlevitsk@redhat.com> writes:

> 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 it while it
> is in use.
>
> Fixes: 61e5f69ef0837 ("KVM: x86: implement KVM_GUESTDBG_BLOCKIRQ")
>
> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> ---
> 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 | 3 +++
> 4 files changed, 8 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..dccf927baa4dd 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10747,6 +10747,9 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
> if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
> vcpu->arch.singlestep_rip = kvm_get_linear_rip(vcpu);
>
> + kvm_request_apicv_update(vcpu->kvm,
> + !(vcpu->guest_debug & KVM_GUESTDBG_BLOCKIRQ),
> + APICV_INHIBIT_REASON_BLOCKIRQ);
> /*
> * Trigger an rflags update that will inject or remove the trace
> * flags.

This fixes the problem for me!

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

--
Vitaly