linux-kernel - Re: [PATCH RFC 3/5] x86: KVM: svm: clear interrupt shadow on all paths in skip_emulated

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Message-ID: <CALMp9eRRqCLKAL4FoZVMk=fHfnrN7EnTVxR___soiHUdrHLAMQ@mail.gmail.com>
Date:   Wed, 31 Jul 2019 16:45:21 -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>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH RFC 3/5] x86: KVM: svm: clear interrupt shadow on all
 paths in skip_emulated_instruction()

On Wed, Jul 31, 2019 at 4:37 PM Sean Christopherson
<sean.j.christopherson@...el.com> wrote:

> At a glance, the full emulator models behavior correctly, e.g. see
> toggle_interruptibility() and setters of ctxt->interruptibility.
>
> I'm pretty sure that leaves the EPT misconfig MMIO and APIC access EOI
> fast paths as the only (VMX) path that would incorrectly handle a
> MOV/POP SS.  Reading the guest's instruction stream to detect MOV/POP SS
> would defeat the whole "fast path" thing, not to mention both paths aren't
> exactly architecturally compliant in the first place.

The proposed patch clears the interrupt shadow in the VMCB on all
paths through svm's skip_emulated_instruction. If this happens at the
tail end of emulation, it doesn't matter if the full emulator does the
right thing.