linux-kernel - [PATCH 3.16 005/254] KVM: x86: Don't re-execute instruction when not passing CR2 value

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Message-ID: <lsq.1519831218.454718217@decadent.org.uk>
Date:   Wed, 28 Feb 2018 15:20:18 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Nikita Leshenko" <nikita.leshchenko@...cle.com>,
        "Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
        "Liran Alon" <liran.alon@...cle.com>,
        "Wanpeng Li" <wanpeng.li@...mail.com>,
        "Radim Krčmář" <rkrcmar@...hat.com>
Subject: [PATCH 3.16 005/254] KVM: x86: Don't re-execute instruction when
 not passing CR2 value

3.16.55-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Liran Alon <liran.alon@...cle.com>

commit 9b8ae63798cb97e785a667ff27e43fa6220cb734 upstream.

In case of instruction-decode failure or emulation failure,
x86_emulate_instruction() will call reexecute_instruction() which will
attempt to use the cr2 value passed to x86_emulate_instruction().
However, when x86_emulate_instruction() is called from
emulate_instruction(), cr2 is not passed (passed as 0) and therefore
it doesn't make sense to execute reexecute_instruction() logic at all.

Fixes: 51d8b66199e9 ("KVM: cleanup emulate_instruction")

Signed-off-by: Liran Alon <liran.alon@...cle.com>
Reviewed-by: Nikita Leshenko <nikita.leshchenko@...cle.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Reviewed-by: Wanpeng Li <wanpeng.li@...mail.com>
Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/include/asm/kvm_host.h | 3 ++-
 arch/x86/kvm/vmx.c              | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -847,7 +847,8 @@ int x86_emulate_instruction(struct kvm_v
 static inline int emulate_instruction(struct kvm_vcpu *vcpu,
 			int emulation_type)
 {
-	return x86_emulate_instruction(vcpu, 0, emulation_type, NULL, 0);
+	return x86_emulate_instruction(vcpu, 0,
+			emulation_type | EMULTYPE_NO_REEXECUTE, NULL, 0);
 }
 
 void kvm_enable_efer_bits(u64);
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -5659,7 +5659,7 @@ static int handle_invalid_guest_state(st
 		if (test_bit(KVM_REQ_EVENT, &vcpu->requests))
 			return 1;
 
-		err = emulate_instruction(vcpu, EMULTYPE_NO_REEXECUTE);
+		err = emulate_instruction(vcpu, 0);
 
 		if (err == EMULATE_USER_EXIT) {
 			++vcpu->stat.mmio_exits;