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

[David Hildenbrand]

On 11.08.2017 08:13, Paolo Bonzini wrote:
> On 11/08/2017 07:59, Wanpeng Li wrote:
>> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>>
>> 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 */

> because AMD gets here even if npt=1.
> 
> Paolo

-- 

Thanks,

David