KVM: nVMX: Don't reread VMCS-agnostic state when switching VMCS

When switching between vmcs01 and vmcs02, there is no need to update
state tracking for values that aren't tied to any particular VMCS as
the per-vCPU values are already up-to-date (vmx_switch_vmcs() can only
be called when the vCPU is loaded).

Avoiding the update eliminates a RDMSR, and potentially a RDPKRU and
posted-interrupt update (cmpxchg64() and more).
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -279,7 +279,7 @@ static void vmx_switch_vmcs(struct kvm_vcpu *vcpu, struct loaded_vmcs *vmcs)
 	cpu = get_cpu();
 	prev = vmx->loaded_vmcs;
 	vmx->loaded_vmcs = vmcs;
-	vmx_vcpu_load(vcpu, cpu);
+	vmx_vcpu_load_vmcs(vcpu, cpu);
 	vmx_sync_vmcs_host_state(vmx, prev);
 	put_cpu();
 

arch/x86/kvm/vmx/vmx.c

@@ -1234,11 +1234,7 @@ static void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
 		pi_set_on(pi_desc);
 }
 
-/*
- * Switches to specified vcpu, until a matching vcpu_put(), but assumes
- * vcpu mutex is already taken.
- */
-void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
+void vmx_vcpu_load_vmcs(struct kvm_vcpu *vcpu, int cpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	bool already_loaded = vmx->loaded_vmcs->cpu == cpu;
@@ -1299,8 +1295,20 @@ void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	if (kvm_has_tsc_control &&
 	    vmx->current_tsc_ratio != vcpu->arch.tsc_scaling_ratio)
 		decache_tsc_multiplier(vmx);
+}
+
+/*
+ * Switches to specified vcpu, until a matching vcpu_put(), but assumes
+ * vcpu mutex is already taken.
+ */
+void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
+{
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
+
+	vmx_vcpu_load_vmcs(vcpu, cpu);
 
 	vmx_vcpu_pi_load(vcpu, cpu);
+
 	vmx->host_pkru = read_pkru();
 	vmx->host_debugctlmsr = get_debugctlmsr();
 }

arch/x86/kvm/vmx/vmx.h

@@ -302,6 +302,7 @@ struct kvm_vmx {
 };
 
 bool nested_vmx_allowed(struct kvm_vcpu *vcpu);
+void vmx_vcpu_load_vmcs(struct kvm_vcpu *vcpu, int cpu);
 void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu);
 int allocate_vpid(void);
 void free_vpid(int vpid);