linux-kernel - Re: [PATCH RFC 1/5] x86: KVM: svm: don't pretend to advance RIP in case wrmsr

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Message-ID: <87r27nfhxg.fsf@vitty.brq.redhat.com>
Date:   Fri, 21 Jun 2019 10:42:35 +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 1/5] x86: KVM: svm: don't pretend to advance RIP in case wrmsr_interception() results in #GP

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

> On Thu, Jun 20, 2019 at 4:02 AM Vitaly Kuznetsov <vkuznets@...hat.com> wrote:
>>
>> svm->next_rip is only used by skip_emulated_instruction() and in case
>> kvm_set_msr() fails we rightfully don't do that. Move svm->next_rip
>> advancement to 'else' branch to avoid creating false impression that
>> it's always advanced.
>>
>> By the way, rdmsr_interception() has it right already.
>
> I think I actually prefer the current placement, because this allows
> the code that's common to both kvm-amd.ko and kvm-intel.ko to be
> hoisted into the vendor-agnostic kvm module. Also, this hard-coded '2'
> should be going away, right?

This whole change goes away in PATCH5 (with hardcoded '+2'), I added
this patch just to make it clear that RIP advancement we're doing here
is only being used by kvm_skip_emulated_instruction() and
kvm_inject_gp() branch is not affected.

We can throw this patch away from the series.

-- 
Vitaly