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

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@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 35 insertions, 0 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d1cfe204f0e2..96158ffebefd 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1439,6 +1439,41 @@ 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
  */