[PATCH 2/2] KVM: x86: Add kvm_emulate_{rd,wr}msr() to consolidate VXM/SVM code

[Sean Christopherson]

Move RDMSR and WRMSR emulation into common x86 code to consolidate
nearly identical SVM and VMX code.

Note, consolidating RDMSR introduces an extra indirect call, i.e.
retpoline, due to reaching {svm,vmx}_get_msr() via kvm_x86_ops, but a
guest kernel likely has bigger problems if increasing the latency of
RDMSR VM-Exits by ~70 cycles has a measurable impact on overall VM
performance.  E.g. the only recurring RDMSR VM-Exits (after booting) on
my system running Linux 5.2 in the guest are for MSR_IA32_TSC_ADJUST via
arch_cpu_idle_enter().

No functional change intended.

Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h |  2 ++
 arch/x86/kvm/svm.c              | 29 ++-------------------------
 arch/x86/kvm/vmx/vmx.c          | 29 ++-------------------------
 arch/x86/kvm/x86.c              | 35 +++++++++++++++++++++++++++++++++
 4 files changed, 41 insertions(+), 54 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 649d80b5cd6f..003c1cc8e28b 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1328,6 +1328,8 @@ void kvm_enable_efer_bits(u64);
 bool kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer);
 int kvm_get_msr(struct kvm_vcpu *vcpu, u32 index, u64 *data);
 int kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data);
+int kvm_emulate_rdmsr(struct kvm_vcpu *vcpu);
+int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu);
 
 struct x86_emulate_ctxt;
 
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 030bc9f7b7a7..b033aebbcd30 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -4220,22 +4220,7 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 
 static int rdmsr_interception(struct vcpu_svm *svm)
 {
-	u32 ecx = kvm_rcx_read(&svm->vcpu);
-	struct msr_data msr_info;
-
-	msr_info.index = ecx;
-	msr_info.host_initiated = false;
-	if (svm_get_msr(&svm->vcpu, &msr_info)) {
-		trace_kvm_msr_read_ex(ecx);
-		kvm_inject_gp(&svm->vcpu, 0);
-		return 1;
-	} else {
-		trace_kvm_msr_read(ecx, msr_info.data);
-
-		kvm_rax_write(&svm->vcpu, msr_info.data & 0xffffffff);
-		kvm_rdx_write(&svm->vcpu, msr_info.data >> 32);
-		return kvm_skip_emulated_instruction(&svm->vcpu);
-	}
+	return kvm_emulate_rdmsr(&svm->vcpu);
 }
 
 static int svm_set_vm_cr(struct kvm_vcpu *vcpu, u64 data)
@@ -4425,17 +4410,7 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 
 static int wrmsr_interception(struct vcpu_svm *svm)
 {
-	u32 ecx = kvm_rcx_read(&svm->vcpu);
-	u64 data = kvm_read_edx_eax(&svm->vcpu);
-
-	if (kvm_set_msr(&svm->vcpu, ecx, data)) {
-		trace_kvm_msr_write_ex(ecx, data);
-		kvm_inject_gp(&svm->vcpu, 0);
-		return 1;
-	} else {
-		trace_kvm_msr_write(ecx, data);
-		return kvm_skip_emulated_instruction(&svm->vcpu);
-	}
+	return kvm_emulate_wrmsr(&svm->vcpu);
 }
 
 static int msr_interception(struct vcpu_svm *svm)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index f4f4114e756f..b98a88dc8ca6 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4866,37 +4866,12 @@ static int handle_cpuid(struct kvm_vcpu *vcpu)
 
 static int handle_rdmsr(struct kvm_vcpu *vcpu)
 {
-	u32 ecx = kvm_rcx_read(vcpu);
-	struct msr_data msr_info;
-
-	msr_info.index = ecx;
-	msr_info.host_initiated = false;
-	if (vmx_get_msr(vcpu, &msr_info)) {
-		trace_kvm_msr_read_ex(ecx);
-		kvm_inject_gp(vcpu, 0);
-		return 1;
-	}
-
-	trace_kvm_msr_read(ecx, msr_info.data);
-
-	kvm_rax_write(vcpu, msr_info.data & -1u);
-	kvm_rdx_write(vcpu, (msr_info.data >> 32) & -1u);
-	return kvm_skip_emulated_instruction(vcpu);
+	return kvm_emulate_rdmsr(vcpu);
 }
 
 static int handle_wrmsr(struct kvm_vcpu *vcpu)
 {
-	u32 ecx = kvm_rcx_read(vcpu);
-	u64 data = kvm_read_edx_eax(vcpu);
-
-	if (kvm_set_msr(vcpu, ecx, data) != 0) {
-		trace_kvm_msr_write_ex(ecx, data);
-		kvm_inject_gp(vcpu, 0);
-		return 1;
-	}
-
-	trace_kvm_msr_write(ecx, data);
-	return kvm_skip_emulated_instruction(vcpu);
+	return kvm_emulate_wrmsr(vcpu);
 }
 
 static int handle_tpr_below_threshold(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a67730600803..7cd578d52611 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1434,6 +1434,41 @@ int kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data)
 }
 EXPORT_SYMBOL_GPL(kvm_set_msr);
 
+int kvm_emulate_rdmsr(struct kvm_vcpu *vcpu)
+{
+	u32 ecx = kvm_rcx_read(vcpu);
+	u64 data;
+
+	if (kvm_get_msr(vcpu, ecx, &data)) {
+		trace_kvm_msr_read_ex(ecx);
+		kvm_inject_gp(vcpu, 0);
+		return 1;
+	}
+
+	trace_kvm_msr_read(ecx, data);
+
+	kvm_rax_write(vcpu, data & -1u);
+	kvm_rdx_write(vcpu, (data >> 32) & -1u);
+	return kvm_skip_emulated_instruction(vcpu);
+}
+EXPORT_SYMBOL_GPL(kvm_emulate_rdmsr);
+
+int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu)
+{
+	u32 ecx = kvm_rcx_read(vcpu);
+	u64 data = kvm_read_edx_eax(vcpu);
+
+	if (kvm_set_msr(vcpu, ecx, data)) {
+		trace_kvm_msr_write_ex(ecx, data);
+		kvm_inject_gp(vcpu, 0);
+		return 1;
+	}
+
+	trace_kvm_msr_write(ecx, data);
+	return kvm_skip_emulated_instruction(vcpu);
+}
+EXPORT_SYMBOL_GPL(kvm_emulate_wrmsr);
+
 /*
  * Adapt set_msr() to msr_io()'s calling convention
  */
-- 
2.22.0