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: <87ftmm71p3.fsf@vitty.brq.redhat.com>
Date:   Wed, 31 Jul 2019 15:50:32 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        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()

Jim Mattson <jmattson@...gle.com> writes:

> On Thu, Jun 20, 2019 at 4:02 AM Vitaly Kuznetsov <vkuznets@...hat.com> wrote:
>>
>> Regardless of the way how we skip instruction, interrupt shadow needs to be
>> cleared.
>
> This change is definitely an improvement, but the existing code seems
> to assume that we never call skip_emulated_instruction on a
> POP-SS/MOV-to-SS/STI. Is that enforced anywhere?

(before I send v1 of the series) I looked at the current code and I
don't think it is enforced, however, VMX version does the same and
honestly I can't think of a situation when we would be doing 'skip' for
such an instruction.... and there's nothing we can easily enforce from
skip_emulated_instruction() as we have no idea what the instruction
is... 

I can of course be totally wrong and would appreciate if someone more
knowledgeable chimes in :-)

-- 
Vitaly