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

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Message-ID: <b35c8b24-7531-5a5d-1518-eaf9567359ae@redhat.com>
Date:   Wed, 11 Sep 2019 17:51:05 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jan Dakinevich <jan.dakinevich@...tuozzo.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     Denis Lunev <den@...tuozzo.com>,
        Roman Kagan <rkagan@...tuozzo.com>,
        Denis Plotnikov <dplotnikov@...tuozzo.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.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 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.

Paolo