linux-kernel - Re: [PATCH 0/3] fix emulation error on Windows bootup

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Message-ID: <4a4c71d8-c29a-d04c-e7d3-4ea9ec916a29@redhat.com>
Date:   Fri, 13 Sep 2019 11:51:37 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Jan Dakinevich <jan.dakinevich@...tuozzo.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Denis Lunev <den@...tuozzo.com>,
        Roman Kagan <rkagan@...tuozzo.com>,
        Denis Plotnikov <dplotnikov@...tuozzo.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH 0/3] fix emulation error on Windows bootup

On 11/09/19 21:53, Sean Christopherson wrote:
> On Wed, Sep 11, 2019 at 05:51:05PM +0200, Paolo Bonzini wrote:
>> On 27/08/19 15:07, Jan Dakinevich wrote:
>>> This series intended to fix (again) a bug that was a subject of the 
>>> following change:
>>>
>>>   6ea6e84 ("KVM: x86: inject exceptions produced by x86_decode_insn")
>>>
>>> Suddenly, that fix had a couple mistakes. First, ctxt->have_exception was 
>>> not set if fault happened during instruction decoding. Second, returning 
>>> value of inject_emulated_instruction was used to make the decision to 
>>> reenter guest, but this could happen iff on nested page fault, that is not 
>>> the scope where this bug could occur.
>>>
>>> However, I have still deep doubts about 3rd commit in the series. Could
>>> you please, make me an advise if it is the correct handling of guest page 
>>> fault?
>>>
>>> Jan Dakinevich (3):
>>>   KVM: x86: fix wrong return code
>>>   KVM: x86: set ctxt->have_exception in x86_decode_insn()
>>>   KVM: x86: always stop emulation on page fault
>>>
>>>  arch/x86/kvm/emulate.c | 4 +++-
>>>  arch/x86/kvm/x86.c     | 4 +++-
>>>  2 files changed, 6 insertions(+), 2 deletions(-)
>>>
>>
>> Queued, thanks.  I added the WARN_ON_ONCE that Sean suggested.
> 
> Which version did you queue?  It sounds like you queued v1, which breaks
> VMware backdoor emulation due to incorrect patch ordering.  v3[*] fixes
> the ordering issue and adds the WARN_ON_ONCE.

I applied v1 with all the fixes, then found out v3 existed and replaced
with it (but still added a comment).

Paolo