linux-kernel - Re: [PATCH v3] KVM: MMU: Fix guest stuck during boot due to read/write emulation against GVA

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Message-ID: <f2bd387f-93c8-795d-307a-9eb9729b0e60@redhat.com>
Date:   Fri, 11 Aug 2017 08:53:46 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v3] KVM: MMU: Fix guest stuck during boot due to
 read/write emulation against GVA

On 11.08.2017 08:46, 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 setting the gpa_available flag under direct mode.  
> 
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Cc: Brijesh Singh <brijesh.singh@....com>
> Cc: David Hildenbrand <david@...hat.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
> ---
>  arch/x86/kvm/mmu.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 849312d..4780348 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -3791,8 +3791,11 @@ 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;
> +		/* With shadow page tables, cr2 could contain a GVA, not a GPA */
> +		if (vcpu->arch.mmu.direct_map) {
> +			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;
> 

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 

Thanks,

David