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Date:	Thu, 19 Jun 2014 09:59:35 -0400
From:	"Gabriel L. Somlo" <gsomlo@...il.com>
To:	KVM <kvm@...r.kernel.org>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	Gleb Natapov <gleb@...nel.org>,
	Eric Northup <digitaleric@...gle.com>,
	Nadav Amit <namit@...technion.ac.il>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	nadav.amit@...il.com, joro@...tes.org, agraf@...e.de
Subject: [PATCH] Revert "kvm: x86: emulate monitor and mwait instructions as
 nop"

This reverts commit 87c00572ba05aa8c9db118da75c608f47eb10b9e.

OS X <= 10.7.* are the only known guests which realistically required
this functionality. As it turns out, OS X can be told to forego using
monitor/mwait by passing it "idlehalt=0" as a kernel argument, so we're
better off removing this hack from KVM altogether, at least for now.

Signed-off-by: Gabriel L. Somlo <somlo@....edu>
Acked-by: Michael S. Tsirkin <mst@...hat.com>
---

OK, here's the formal proposal to revert my original monitor/mwait hack...
I wish I knew about the "idlehalt=0" before I submitted it, but such is life.
Depending on how those of you higher up the food chain feel, I can tolerate
leaving the hack in if it's never on by default (i.e. no CPUID advertisement),
but would feel better if we could simply undo this until we have a better
solution, something less controversial...

Thanks, and sorry for all the noise,
  Gabriel

 arch/x86/kvm/cpuid.c |  2 --
 arch/x86/kvm/svm.c   | 28 ++++++++--------------------
 arch/x86/kvm/vmx.c   | 20 ++++----------------
 3 files changed, 12 insertions(+), 38 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 38a0afe..17b42fa 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -283,8 +283,6 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 		0 /* Reserved */ | f_lm | F(3DNOWEXT) | F(3DNOW);
 	/* cpuid 1.ecx */
 	const u32 kvm_supported_word4_x86_features =
-		/* NOTE: MONITOR (and MWAIT) are emulated as NOP,
-		 * but *not* advertised to guests via CPUID ! */
 		F(XMM3) | F(PCLMULQDQ) | 0 /* DTES64, MONITOR */ |
 		0 /* DS-CPL, VMX, SMX, EST */ |
 		0 /* TM2 */ | F(SSSE3) | 0 /* CNXT-ID */ | 0 /* Reserved */ |
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index ec8366c..6b88b6a 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -2763,6 +2763,12 @@ static int xsetbv_interception(struct vcpu_svm *svm)
 	return 1;
 }
 
+static int invalid_op_interception(struct vcpu_svm *svm)
+{
+	kvm_queue_exception(&svm->vcpu, UD_VECTOR);
+	return 1;
+}
+
 static int task_switch_interception(struct vcpu_svm *svm)
 {
 	u16 tss_selector;
@@ -3274,24 +3280,6 @@ static int pause_interception(struct vcpu_svm *svm)
 	return 1;
 }
 
-static int nop_interception(struct vcpu_svm *svm)
-{
-	skip_emulated_instruction(&(svm->vcpu));
-	return 1;
-}
-
-static int monitor_interception(struct vcpu_svm *svm)
-{
-	printk_once(KERN_WARNING "kvm: MONITOR instruction emulated as NOP!\n");
-	return nop_interception(svm);
-}
-
-static int mwait_interception(struct vcpu_svm *svm)
-{
-	printk_once(KERN_WARNING "kvm: MWAIT instruction emulated as NOP!\n");
-	return nop_interception(svm);
-}
-
 static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = {
 	[SVM_EXIT_READ_CR0]			= cr_interception,
 	[SVM_EXIT_READ_CR3]			= cr_interception,
@@ -3349,8 +3337,8 @@ static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = {
 	[SVM_EXIT_CLGI]				= clgi_interception,
 	[SVM_EXIT_SKINIT]			= skinit_interception,
 	[SVM_EXIT_WBINVD]                       = emulate_on_interception,
-	[SVM_EXIT_MONITOR]			= monitor_interception,
-	[SVM_EXIT_MWAIT]			= mwait_interception,
+	[SVM_EXIT_MONITOR]			= invalid_op_interception,
+	[SVM_EXIT_MWAIT]			= invalid_op_interception,
 	[SVM_EXIT_XSETBV]			= xsetbv_interception,
 	[SVM_EXIT_NPF]				= pf_interception,
 };
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 801332e..163958f 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -5672,24 +5672,12 @@ static int handle_pause(struct kvm_vcpu *vcpu)
 	return 1;
 }
 
-static int handle_nop(struct kvm_vcpu *vcpu)
+static int handle_invalid_op(struct kvm_vcpu *vcpu)
 {
-	skip_emulated_instruction(vcpu);
+	kvm_queue_exception(vcpu, UD_VECTOR);
 	return 1;
 }
 
-static int handle_mwait(struct kvm_vcpu *vcpu)
-{
-	printk_once(KERN_WARNING "kvm: MWAIT instruction emulated as NOP!\n");
-	return handle_nop(vcpu);
-}
-
-static int handle_monitor(struct kvm_vcpu *vcpu)
-{
-	printk_once(KERN_WARNING "kvm: MONITOR instruction emulated as NOP!\n");
-	return handle_nop(vcpu);
-}
-
 /*
  * To run an L2 guest, we need a vmcs02 based on the L1-specified vmcs12.
  * We could reuse a single VMCS for all the L2 guests, but we also want the
@@ -6651,8 +6639,8 @@ static int (*const kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
 	[EXIT_REASON_EPT_VIOLATION]	      = handle_ept_violation,
 	[EXIT_REASON_EPT_MISCONFIG]           = handle_ept_misconfig,
 	[EXIT_REASON_PAUSE_INSTRUCTION]       = handle_pause,
-	[EXIT_REASON_MWAIT_INSTRUCTION]	      = handle_mwait,
-	[EXIT_REASON_MONITOR_INSTRUCTION]     = handle_monitor,
+	[EXIT_REASON_MWAIT_INSTRUCTION]	      = handle_invalid_op,
+	[EXIT_REASON_MONITOR_INSTRUCTION]     = handle_invalid_op,
 	[EXIT_REASON_INVEPT]                  = handle_invept,
 };
 
-- 
1.9.3

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