[PATCH] KVM: selftests: Verify KVM_MSR_EXIT_REASON_INVAL on reserved EFER write

[Tharit Tangkijwanichakul]

The msr_filter_deny test covers the FILTER and UNKNOWN MSR exit
reasons, but nothing exercises KVM_MSR_EXIT_REASON_INVAL.

Have the guest set a reserved bit (bit 63) in EFER while preserving
the other bits, and verify that the write exits to userspace with
KVM_MSR_EXIT_REASON_INVAL along with the attempted value.

Signed-off-by: Tharit Tangkijwanichakul <tharitt97@xxxxxxxxx>
---
Tested on Intel Core i5-10210U (VMX). Not tested on AMD.
---
 .../selftests/kvm/x86/userspace_msr_exit_test.c      | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/kvm/x86/userspace_msr_exit_test.c b/tools/testing/selftests/kvm/x86/userspace_msr_exit_test.c
index 2808ce727e5f..7446e1404264 100644
--- a/tools/testing/selftests/kvm/x86/userspace_msr_exit_test.c
+++ b/tools/testing/selftests/kvm/x86/userspace_msr_exit_test.c
@@ -309,6 +309,9 @@ static void guest_msr_calls(bool trapped)
 	/* Invalid MSR, should always be handled by user space exit */
 	GUEST_ASSERT(rdmsr(0xdeadbeef) == 0xdeadbeef);
 	wrmsr(0xdeadbeef, 0x1234);
+
+	/* Setting a reserved EFER bit is rejected by KVM, exit with INVAL */
+	wrmsr(MSR_EFER, rdmsr(MSR_EFER) | BIT_ULL(63));
 }
 
 static void guest_code_filter_deny(void)
@@ -627,6 +630,13 @@ static void handle_wrmsr(struct kvm_run *run)
 		TEST_ASSERT(run->msr.reason == KVM_MSR_EXIT_REASON_UNKNOWN,
 			    "deadbeef trap w/o inval fault");
 	}
+
+	if (run->msr.index == MSR_EFER) {
+		TEST_ASSERT(run->msr.data & BIT_ULL(63),
+			    "MSR_EFER data missing reserved bit");
+		TEST_ASSERT(run->msr.reason == KVM_MSR_EXIT_REASON_INVAL,
+			    "MSR_EFER trap w/o inval fault");
+	}
 }
 
 KVM_ONE_VCPU_TEST(user_msr, msr_filter_deny, guest_code_filter_deny)
@@ -667,7 +677,7 @@ KVM_ONE_VCPU_TEST(user_msr, msr_filter_deny, guest_code_filter_deny)
 
 done:
 	TEST_ASSERT(msr_reads == 4, "Handled 4 rdmsr in user space");
-	TEST_ASSERT(msr_writes == 3, "Handled 3 wrmsr in user space");
+	TEST_ASSERT(msr_writes == 5, "Handled 5 wrmsr in user space");
 }
 
 KVM_ONE_VCPU_TEST(user_msr, msr_permission_bitmap, guest_code_permission_bitmap)
-- 
2.53.0