KVM: x86: Refactor kvm_get_feature_msr() to avoid struct kvm_msr_entry

Refactor kvm_get_feature_msr() to take the components of kvm_msr_entry as
separate parameters, along with a vCPU pointer, i.e. to give it the same
prototype as kvm_{g,s}et_msr_ignored_check().  This will allow using a
common inner helper for handling accesses to "regular" and feature MSRs.

No functional change intended.

Link: https://lore.kernel.org/r/20240802181935.292540-7-seanjc@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/x86.c

@@ -1659,39 +1659,38 @@ static u64 kvm_get_arch_capabilities(void)
 	return data;
 }
 
-static int kvm_get_feature_msr(struct kvm_msr_entry *msr)
+static int kvm_get_feature_msr(struct kvm_vcpu *vcpu, u32 index, u64 *data,
+			       bool host_initiated)
 {
-	switch (msr->index) {
+	WARN_ON_ONCE(!host_initiated);
+
+	switch (index) {
 	case MSR_IA32_ARCH_CAPABILITIES:
-		msr->data = kvm_get_arch_capabilities();
+		*data = kvm_get_arch_capabilities();
 		break;
 	case MSR_IA32_PERF_CAPABILITIES:
-		msr->data = kvm_caps.supported_perf_cap;
+		*data = kvm_caps.supported_perf_cap;
 		break;
 	case MSR_IA32_UCODE_REV:
-		rdmsrl_safe(msr->index, &msr->data);
+		rdmsrl_safe(index, data);
 		break;
 	default:
-		return kvm_x86_call(get_feature_msr)(msr->index, &msr->data);
+		return kvm_x86_call(get_feature_msr)(index, data);
 	}
 	return 0;
 }
 
 static int do_get_feature_msr(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
 {
-	struct kvm_msr_entry msr;
 	int r;
 
 	/* Unconditionally clear the output for simplicity */
-	msr.data = 0;
-	msr.index = index;
-	r = kvm_get_feature_msr(&msr);
+	*data = 0;
+	r = kvm_get_feature_msr(vcpu, index, data, true);
 
 	if (r == KVM_MSR_RET_UNSUPPORTED && kvm_msr_ignored_check(index, 0, false))
 		r = 0;
 
-	*data = msr.data;
-
 	return r;
 }
 
@@ -7378,11 +7377,9 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
 
 static void kvm_probe_feature_msr(u32 msr_index)
 {
-	struct kvm_msr_entry msr = {
-		.index = msr_index,
-	};
+	u64 data;
 
-	if (kvm_get_feature_msr(&msr))
+	if (kvm_get_feature_msr(NULL, msr_index, &data, true))
 		return;
 
 	msr_based_features[num_msr_based_features++] = msr_index;