KVM: VMX: Use accessors for GPRs outside of dedicated caching logic

... now that there is no overhead when using dedicated accessors.

Opportunistically remove a bogus "FIXME" in handle_rdmsr() regarding
the upper 32 bits of RAX and RDX.  Zeroing the upper 32 bits is
architecturally correct as 32-bit writes in 64-bit mode unconditionally
clear the upper 32 bits.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -4764,7 +4764,7 @@ static int handle_invvpid(struct kvm_vcpu *vcpu)
 static int nested_vmx_eptp_switching(struct kvm_vcpu *vcpu,
 				     struct vmcs12 *vmcs12)
 {
-	u32 index = vcpu->arch.regs[VCPU_REGS_RCX];
+	u32 index = kvm_rcx_read(vcpu);
 	u64 address;
 	bool accessed_dirty;
 	struct kvm_mmu *mmu = vcpu->arch.walk_mmu;
@@ -4810,7 +4810,7 @@ static int handle_vmfunc(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	struct vmcs12 *vmcs12;
-	u32 function = vcpu->arch.regs[VCPU_REGS_RAX];
+	u32 function = kvm_rax_read(vcpu);
 
 	/*
 	 * VMFUNC is only supported for nested guests, but we always enable the
@@ -4896,7 +4896,7 @@ static bool nested_vmx_exit_handled_io(struct kvm_vcpu *vcpu,
 static bool nested_vmx_exit_handled_msr(struct kvm_vcpu *vcpu,
 	struct vmcs12 *vmcs12, u32 exit_reason)
 {
-	u32 msr_index = vcpu->arch.regs[VCPU_REGS_RCX];
+	u32 msr_index = kvm_rcx_read(vcpu);
 	gpa_t bitmap;
 
 	if (!nested_cpu_has(vmcs12, CPU_BASED_USE_MSR_BITMAPS))

arch/x86/kvm/vmx/vmx.c

@@ -4831,7 +4831,7 @@ static int handle_cpuid(struct kvm_vcpu *vcpu)
 
 static int handle_rdmsr(struct kvm_vcpu *vcpu)
 {
-	u32 ecx = vcpu->arch.regs[VCPU_REGS_RCX];
+	u32 ecx = kvm_rcx_read(vcpu);
 	struct msr_data msr_info;
 
 	msr_info.index = ecx;
@@ -4844,18 +4844,16 @@ static int handle_rdmsr(struct kvm_vcpu *vcpu)
 
 	trace_kvm_msr_read(ecx, msr_info.data);
 
-	/* FIXME: handling of bits 32:63 of rax, rdx */
-	vcpu->arch.regs[VCPU_REGS_RAX] = msr_info.data & -1u;
-	vcpu->arch.regs[VCPU_REGS_RDX] = (msr_info.data >> 32) & -1u;
+	kvm_rax_write(vcpu, msr_info.data & -1u);
+	kvm_rdx_write(vcpu, (msr_info.data >> 32) & -1u);
 	return kvm_skip_emulated_instruction(vcpu);
 }
 
 static int handle_wrmsr(struct kvm_vcpu *vcpu)
 {
 	struct msr_data msr;
-	u32 ecx = vcpu->arch.regs[VCPU_REGS_RCX];
-	u64 data = (vcpu->arch.regs[VCPU_REGS_RAX] & -1u)
-		| ((u64)(vcpu->arch.regs[VCPU_REGS_RDX] & -1u) << 32);
+	u32 ecx = kvm_rcx_read(vcpu);
+	u64 data = kvm_read_edx_eax(vcpu);
 
 	msr.data = data;
 	msr.index = ecx;