linux-kernel - [PATCH 3.2 002/140] KVM: VMX: do not try to reexecute failed instruction while emulating invalid guest state

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Message-ID: <lsq.1519831221.481945703@decadent.org.uk>
Date:   Wed, 28 Feb 2018 15:20:21 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Gleb Natapov" <gleb@...hat.com>
Subject: [PATCH 3.2 002/140] KVM: VMX: do not try to reexecute failed
 instruction while emulating invalid guest state

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

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

From: Gleb Natapov <gleb@...hat.com>

commit 991eebf9f8e523e7ff1e4d31ac80641582b2e57a upstream.

During invalid guest state emulation vcpu cannot enter guest mode to try
to reexecute instruction that emulator failed to emulate, so emulation
will happen again and again.  Prevent that by telling the emulator that
instruction reexecution should not be attempted.

Signed-off-by: Gleb Natapov <gleb@...hat.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -694,6 +694,7 @@ enum emulation_result {
 #define EMULTYPE_NO_DECODE	    (1 << 0)
 #define EMULTYPE_TRAP_UD	    (1 << 1)
 #define EMULTYPE_SKIP		    (1 << 2)
+#define EMULTYPE_NO_REEXECUTE	    (1 << 4)
 int x86_emulate_instruction(struct kvm_vcpu *vcpu, unsigned long cr2,
 			    int emulation_type, void *insn, int insn_len);
 
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -4891,7 +4891,7 @@ static int handle_invalid_guest_state(st
 		    && (kvm_get_rflags(&vmx->vcpu) & X86_EFLAGS_IF))
 			return handle_interrupt_window(&vmx->vcpu);
 
-		err = emulate_instruction(vcpu, 0);
+		err = emulate_instruction(vcpu, EMULTYPE_NO_REEXECUTE);
 
 		if (err == EMULATE_DO_MMIO) {
 			ret = 0;
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4888,10 +4888,14 @@ static int handle_emulation_failure(stru
 	return r;
 }
 
-static bool reexecute_instruction(struct kvm_vcpu *vcpu, gva_t gva)
+static bool reexecute_instruction(struct kvm_vcpu *vcpu, gva_t gva,
+				  int emulation_type)
 {
 	gpa_t gpa;
 
+	if (emulation_type & EMULTYPE_NO_REEXECUTE)
+		return false;
+
 	if (tdp_enabled)
 		return false;
 
@@ -4942,7 +4946,7 @@ int x86_emulate_instruction(struct kvm_v
 		if (r != EMULATION_OK)  {
 			if (emulation_type & EMULTYPE_TRAP_UD)
 				return EMULATE_FAIL;
-			if (reexecute_instruction(vcpu, cr2))
+			if (reexecute_instruction(vcpu, cr2, emulation_type))
 				return EMULATE_DONE;
 			if (emulation_type & EMULTYPE_SKIP)
 				return EMULATE_FAIL;
@@ -4969,7 +4973,7 @@ restart:
 		return EMULATE_DONE;
 
 	if (r == EMULATION_FAILED) {
-		if (reexecute_instruction(vcpu, cr2))
+		if (reexecute_instruction(vcpu, cr2, emulation_type))
 			return EMULATE_DONE;
 
 		return handle_emulation_failure(vcpu);