linux-kernel - Re: [PATCH 09/13] KVM: nVMX: Prioritize SMI over nested IRQ/NMI

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Date:   Tue, 28 Apr 2020 15:04:02 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Oliver Upton <oupton@...gle.com>,
        Peter Shier <pshier@...gle.com>
Subject: Re: [PATCH 09/13] KVM: nVMX: Prioritize SMI over nested IRQ/NMI

On Wed, Apr 22, 2020 at 7:26 PM Sean Christopherson
<sean.j.christopherson@...el.com> wrote:
>
> Check for an unblocked SMI in vmx_check_nested_events() so that pending
> SMIs are correctly prioritized over IRQs and NMIs when the latter events
> will trigger VM-Exit.  This also fixes an issue where an SMI that was
> marked pending while processing a nested VM-Enter wouldn't trigger an
> immediate exit, i.e. would be incorrectly delayed until L2 happened to
> take a VM-Exit.
>
> Fixes: 64d6067057d96 ("KVM: x86: stubs for SMM support")
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/vmx/nested.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 1fdaca5fd93d..8c16b190816b 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -3750,6 +3750,12 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu)
>                 return 0;
>         }
>
> +       if (vcpu->arch.smi_pending && !is_smm(vcpu)) {
> +               if (block_nested_events)
> +                       return -EBUSY;
> +               goto no_vmexit;
> +       }
> +

>From the SDM, volume 3:

• System-management interrupts (SMIs), INIT signals, and higher
priority events take priority over MTF VM exits.

I think this block needs to be moved up.