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

[Paolo Bonzini]

On 11/08/2017 08:46, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng...@hotmail.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 <pbonz...@redhat.com>
> Cc: Radim Krčmář <rkrc...@redhat.com>
> Cc: Brijesh Singh <brijesh.si...@amd.com>
> Cc: David Hildenbrand <da...@redhat.com>
> Signed-off-by: Wanpeng Li <wanpeng...@hotmail.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 
> */

A GVA or a nested GPA, more precisely.

> +             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;
> 


Also not enough, we need

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 5fd7ecbf7284..283e94de3853 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -6393,7 +6393,7 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)
        error_code |= (exit_qualification & 0x100) != 0 ?
               PFERR_GUEST_FINAL_MASK : PFERR_GUEST_PAGE_MASK;
 
-       vcpu->arch.gpa_available = true;
+       vcpu->arch.gpa_available = !is_guest_mode(vcpu);
        vcpu->arch.gpa_val = gpa;
        vcpu->arch.exit_qualification = exit_qualification;
 
@@ -6412,7 +6412,7 @@ static int handle_ept_misconfig(struct kvm_vcpu *vcpu)
        }
 
        ret = handle_mmio_page_fault(vcpu, gpa, true);
-       vcpu->arch.gpa_available = true;
+       vcpu->arch.gpa_available = !is_guest_mode(vcpu);
        vcpu->arch.gpa_val = gpa;
        if (likely(ret == RET_MMIO_PF_EMULATE))
                return x86_emulate_instruction(vcpu, gpa, 0, NULL, 0) ==

Paolo