[PATCH 3/3] KVM: x86: correct mwait and monitor emulation

[Nadav Amit]

mwait and monitor are currently handled as nop. Considering this behavior, they
should still be handled correctly, i.e., check execution conditions and generate
exceptions when required. mwait and monitor may also be executed in real-mode
and are not handled in that case.  This patch performs the emulation of
monitor-mwait according to Intel SDM (other than checking whether interrupt can
be used as a break event).

Signed-off-by: Nadav Amit <namit@xxxxxxxxxxxxxxxxx>
---
 arch/x86/kvm/emulate.c | 41 +++++++++++++++++++++++++++++++++++++++--
 arch/x86/kvm/svm.c     | 22 ++--------------------
 arch/x86/kvm/vmx.c     | 27 +++++++++++----------------
 3 files changed, 52 insertions(+), 38 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index ef7a5a0..424b58d 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3344,6 +3344,43 @@ static int em_bswap(struct x86_emulate_ctxt *ctxt)
 	return X86EMUL_CONTINUE;
 }
 
+static int em_monitor(struct x86_emulate_ctxt *ctxt)
+{
+	int rc;
+	struct segmented_address addr;
+	u64 rcx = reg_read(ctxt, VCPU_REGS_RCX);
+	u64 rax = reg_read(ctxt, VCPU_REGS_RAX);
+	u8 byte;
+
+	if (ctxt->mode != X86EMUL_MODE_PROT64)
+		rcx = (u32)rcx;
+	if (rcx != 0)
+		return emulate_gp(ctxt, 0);
+
+	addr.seg = seg_override(ctxt);
+	addr.ea = ctxt->ad_bytes == 8 ? rax : (u32)rax;
+	rc = segmented_read(ctxt, addr, &byte, 1);
+	if (rc != X86EMUL_CONTINUE)
+		return rc;
+
+	printk_once(KERN_WARNING "kvm: MONITOR instruction emulated as NOP!\n");
+	return X86EMUL_CONTINUE;
+}
+
+static int em_mwait(struct x86_emulate_ctxt *ctxt)
+{
+	u64 rcx = reg_read(ctxt, VCPU_REGS_RCX);
+
+	if (ctxt->mode != X86EMUL_MODE_PROT64)
+		rcx = (u32)rcx;
+	if ((rcx & ~1UL) != 0)
+		return emulate_gp(ctxt, 0);
+
+	/* Accepting interrupt as break event regardless to cpuid */
+	printk_once(KERN_WARNING "kvm: MWAIT instruction emulated as NOP!\n");
+	return X86EMUL_CONTINUE;
+}
+
 static bool valid_cr(int nr)
 {
 	switch (nr) {
@@ -3557,8 +3594,8 @@ static int check_perm_out(struct x86_emulate_ctxt *ctxt)
 		F2bv(((_f) & ~Lock) | DstAcc | SrcImm, _e)
 
 static const struct opcode group7_rm1[] = {
-	DI(SrcNone | Priv, monitor),
-	DI(SrcNone | Priv, mwait),
+	II(SrcNone | Priv | NoBigReal | UDOnPriv, em_monitor, monitor),
+	II(SrcNone | Priv | NoBigReal | UDOnPriv, em_mwait, mwait),
 	N, N, N, N, N, N,
 };
 
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index ec8366c..a524e04 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -3274,24 +3274,6 @@ 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 +3331,8 @@ 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]			= emulate_on_interception,
+	[SVM_EXIT_MWAIT]			= emulate_on_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..7023e71 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -5672,22 +5672,17 @@ static int handle_pause(struct kvm_vcpu *vcpu)
 	return 1;
 }
 
-static int handle_nop(struct kvm_vcpu *vcpu)
+static int handle_emulate(struct kvm_vcpu *vcpu)
 {
-	skip_emulated_instruction(vcpu);
-	return 1;
-}
+	int err = emulate_instruction(vcpu, 0);
 
-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);
+	if (err != EMULATE_DONE) {
+		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+		vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
+		vcpu->run->internal.ndata = 0;
+		return 0;
+	}
+	return 1;
 }
 
 /*
@@ -6651,8 +6646,8 @@ 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_emulate,
+	[EXIT_REASON_MONITOR_INSTRUCTION]     = handle_emulate,
 	[EXIT_REASON_INVEPT]                  = handle_invept,
 };
 
-- 
1.9.1

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