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: <36a9f411-f90c-3ffa-9ee3-6ebee13a763f@redhat.com>
Date:   Wed, 31 Jul 2019 18:37:14 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>
Cc:     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 31/07/19 15:50, Vitaly Kuznetsov wrote:
> 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 agree, I think a comment is worthwhile but we can live with the
limitation.

Paolo