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SubjectRe: [PATCH 4/4] KVM: nSVM: avoid loss of pending IRQ/NMI before entering L2
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On 05.03.20 11:13, Paolo Bonzini wrote:
> This patch reproduces for nSVM the change that was made for nVMX in
> commit b5861e5cf2fc ("KVM: nVMX: Fix loss of pending IRQ/NMI before
> entering L2"). While I do not have a test that breaks without it, I
> cannot see why it would not be necessary since all events are unblocked
> by VMRUN's setting of GIF back to 1.

I suspect, running Jailhouse enable/disable in a tight loop as KVM guest
can stress this fairly well. At least that was the case last time I
tried (4 years ago, or so) - it broke it.

Unfortunately, we have no up-to-date configuration for such a setup.
Some old pieces are lying around here, could try to hand them over if
someone is interested and has the time I lack ATM.

Jan

>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> arch/x86/kvm/svm.c | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 0d773406f7ac..3df62257889a 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -3574,6 +3574,10 @@ static bool nested_vmcb_checks(struct vmcb *vmcb)
> static void enter_svm_guest_mode(struct vcpu_svm *svm, u64 vmcb_gpa,
> struct vmcb *nested_vmcb, struct kvm_host_map *map)
> {
> + bool evaluate_pending_interrupts =
> + is_intercept(svm, INTERCEPT_VINTR) ||
> + is_intercept(svm, INTERCEPT_IRET);
> +
> if (kvm_get_rflags(&svm->vcpu) & X86_EFLAGS_IF)
> svm->vcpu.arch.hflags |= HF_HIF_MASK;
> else
> @@ -3660,7 +3664,21 @@ static void enter_svm_guest_mode(struct vcpu_svm *svm, u64 vmcb_gpa,
>
> svm->nested.vmcb = vmcb_gpa;
>
> + /*
> + * If L1 had a pending IRQ/NMI before executing VMRUN,
> + * which wasn't delivered because it was disallowed (e.g.
> + * interrupts disabled), L0 needs to evaluate if this pending
> + * event should cause an exit from L2 to L1 or be delivered
> + * directly to L2.
> + *
> + * Usually this would be handled by the processor noticing an
> + * IRQ/NMI window request. However, VMRUN can unblock interrupts
> + * by implicitly setting GIF, so force L0 to perform pending event
> + * evaluation by requesting a KVM_REQ_EVENT.
> + */
> enable_gif(svm);
> + if (unlikely(evaluate_pending_interrupts))
> + kvm_make_request(KVM_REQ_EVENT, &svm->vcpu);
>
> mark_all_dirty(svm->vmcb);
> }
>

--
Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux

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