linux-kernel - Re: [PATCH 2/3] KVM: nVMX: fix wrong condition for SPEC_CTRL and PRED

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Date:   Thu, 22 Feb 2018 10:39:15 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        KarimAllah Ahmed <karahmed@...zon.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, stable@...r.kernel.org
Subject: Re: [PATCH 2/3] KVM: nVMX: fix wrong condition for SPEC_CTRL and
 PRED_CMD MSRs

On 22/02/2018 01:07, Jim Mattson wrote:
> On Wed, Feb 21, 2018 at 1:41 PM, Paolo Bonzini <pbonzini@...hat.com> wrote:
>> We need to change the default all-1s bitmap if the MSRs are _not_
>> intercepted.  However, the code was disabling the intercept when it was
>> _enabled_ in the VMCS01.  This is not causing bigger trouble,
>> because vmx_vcpu_run checks the VMCS02's MSR bitmap and would do the
>> right thing even if fed garbage... but it's obviously a bug and it can
>> cause extra MSR reads and writes when running nested guests.
>>
>> Fixes: d28b387fb74da95d69d2615732f50cceb38e9a4d
>> Fixes: 15d45071523d89b3fb7372e2135fbd72f6af9506
>> Cc: x86@...nel.org
>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> Cc: KarimAllah Ahmed <karahmed@...zon.de>
>> Cc: David Woodhouse <dwmw@...zon.co.uk>
>> Cc: Jim Mattson <jmattson@...gle.com>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: Ingo Molnar <mingo@...nel.org>
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> 
> Wasn't this already fixed by 206587a9fb76 ("X86/nVMX: Properly set
> spec_ctrl and pred_cmd before merging MSRs")?

Ouch, yes, and my patch would have no conflicts at all so it would
reintroduce the bug!  Will resend v2 without it.

Paolo