linux-kernel - Re: [PATCH] KVM: MMU: Fix guest stuck during boot due to read/write emulation against GVA

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Message-ID: <CANRm+Cwb-ZT82Y+rqJ-+73WvsXOct=ta+72Xmshvnsixng4qUA@mail.gmail.com>
Date:   Fri, 11 Aug 2017 14:47:40 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH] KVM: MMU: Fix guest stuck during boot due to read/write
 emulation against GVA

2017-08-11 14:40 GMT+08:00 David Hildenbrand <david@...hat.com>:
> On 11.08.2017 08:13, Paolo Bonzini wrote:
>> On 11/08/2017 07:59, Wanpeng Li wrote:
>>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>>
>>> Commit c016004494b0 (KVM: x86: Avoid guest page table walk when gpa_available
>>> is set) avoids the page table walk when cr2 has already contained a valid GPA.
>>> However, that is not the truth if ept == 0 and shadow page table is used. In
>>> this scenario cr2 can just contains a valid GVA. The commit results in guest
>>> stuck during boot due to read/write emulation against GVA instead of GPA of
>>> the guest.
>>>
>>> This patch fixes it by not setting the gpa_available flag if the shadow page table
>>> is used.
>>
>> Yup, I got these on my overnight tests too.  A better fix that I was
>> going to commit today is:
>>
>>                 if (vcpu->arch.mmu.direct_map) {
>>                         vcpu->arch.gpa_available = true;
>>                         vcpu->arch.gpa_val = fault_address;
>>                 }
>>
>
> Makes sense to me. Can we add a comment?
>
> /* with shadow page tables, cr2 could contain a GVA, not a GPA */

Yeah, thanks for the review.

Regards,
Wanpeng Li