linux-kernel - [PATCH v2] KVM: MMU: Fix guest stuck during boot due to read/write emulation against GVA

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Message-Id: <1502433443-4126-1-git-send-email-wanpeng.li@hotmail.com>
Date:   Thu, 10 Aug 2017 23:37:23 -0700
From:   Wanpeng Li <kernellwp@...il.com>
To:     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: [PATCH v2] KVM: MMU: Fix guest stuck during boot due to read/write emulation against GVA

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>
Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
---
 arch/x86/kvm/mmu.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 849312d..a038879 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3791,8 +3791,10 @@ 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;
+		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;
-- 
2.7.4