KVM: selftests: Add KVM_{G,S}ET_ONE_REG coverage to MSRs test

When KVM_{G,S}ET_ONE_REG are supported, verify that MSRs can be accessed
via ONE_REG and through the dedicated MSR ioctls.  For simplicity, run
the test twice, e.g. instead of trying to get MSR values into the exact
right state when switching write methods.

Reviewed-by: Chao Gao <chao.gao@intel.com>
Link: https://lore.kernel.org/r/20250919223258.1604852-49-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

tools/testing/selftests/kvm/x86/msrs_test.c

@@ -200,6 +200,9 @@ static void guest_main(void)
 	}
 }
 
+static bool has_one_reg;
+static bool use_one_reg;
+
 static void host_test_msr(struct kvm_vcpu *vcpu, u64 guest_val)
 {
 	u64 reset_val = msrs[idx].reset_val;
@@ -213,11 +216,21 @@ static void host_test_msr(struct kvm_vcpu *vcpu, u64 guest_val)
 	TEST_ASSERT(val == guest_val, "Wanted 0x%lx from get_msr(0x%x), got 0x%lx",
 		    guest_val, msr, val);
 
-	vcpu_set_msr(vcpu, msr, reset_val);
+	if (use_one_reg)
+		vcpu_set_reg(vcpu, KVM_X86_REG_MSR(msr), reset_val);
+	else
+		vcpu_set_msr(vcpu, msr, reset_val);
 
 	val = vcpu_get_msr(vcpu, msr);
 	TEST_ASSERT(val == reset_val, "Wanted 0x%lx from get_msr(0x%x), got 0x%lx",
 		    reset_val, msr, val);
+
+	if (!has_one_reg)
+		return;
+
+	val = vcpu_get_reg(vcpu, KVM_X86_REG_MSR(msr));
+	TEST_ASSERT(val == reset_val, "Wanted 0x%lx from get_reg(0x%x), got 0x%lx",
+		    reset_val, msr, val);
 }
 
 static void do_vcpu_run(struct kvm_vcpu *vcpu)
@@ -357,5 +370,12 @@ static void test_msrs(void)
 
 int main(void)
 {
+	has_one_reg = kvm_has_cap(KVM_CAP_ONE_REG);
+
 	test_msrs();
+
+	if (has_one_reg) {
+		use_one_reg = true;
+		test_msrs();
+	}
 }