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+CxDG0nB5_rZvTD1MeCT3wRyojwfT==HGAM8xUr6ye+kaA@mail.gmail.com>
Date:   Fri, 11 Aug 2017 14:15:37 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     "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 14:13 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
> 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;
>                 }
>
> because AMD gets here even if npt=1.

Good point, could I post a patch for this?

Regards,
Wanpeng Li

>
> Paolo
>
>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> Cc: Brijesh Singh <brijesh.singh@....com>
>> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
>> ---
>>  arch/x86/kvm/mmu.c | 2 --
>>  1 file changed, 2 deletions(-)
>>
>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>> index 849312d..e4ce20b 100644
>> --- a/arch/x86/kvm/mmu.c
>> +++ b/arch/x86/kvm/mmu.c
>> @@ -3791,8 +3791,6 @@ int kvm_handle_page_fault(struct kvm_vcpu *vcpu, u64 error_code,
>>
>>               if (need_unprotect && kvm_event_needs_reinjection(vcpu))
>>                       kvm_mmu_unprotect_page_virt(vcpu, fault_address);
>> -             vcpu->arch.gpa_available = true;
>> -             vcpu->arch.gpa_val = fault_address;
>>               r = kvm_mmu_page_fault(vcpu, fault_address, error_code, insn,
>>                               insn_len);
>>               break;
>>
>