KVM: selftests: Print out failing MSR and value in vcpu_set_msr()

Reimplement vcpu_set_msr() as a macro and pretty print the failing MSR
(when possible) and the value if KVM_SET_MSRS fails instead of using the
using the standard KVM_IOCTL_ERROR().  KVM_SET_MSRS is somewhat odd in
that it returns the index of the last successful write, i.e. will be
'0' on failure barring an entirely different KVM bug.  And for writing
MSRs, the MSR being written and the value being written are almost always
relevant to the failure, i.e. just saying "failed!" doesn't help debug.

Place the string goo in a separate macro in anticipation of using it to
further expand MSR testing.

Link: https://lore.kernel.org/r/20230311004618.920745-12-seanjc@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>

tools/testing/selftests/kvm/include/x86_64/processor.h

@@ -928,14 +928,30 @@ static inline void vcpu_clear_cpuid_feature(struct kvm_vcpu *vcpu,
 uint64_t vcpu_get_msr(struct kvm_vcpu *vcpu, uint64_t msr_index);
 int _vcpu_set_msr(struct kvm_vcpu *vcpu, uint64_t msr_index, uint64_t msr_value);
 
-static inline void vcpu_set_msr(struct kvm_vcpu *vcpu, uint64_t msr_index,
-				uint64_t msr_value)
-{
-	int r = _vcpu_set_msr(vcpu, msr_index, msr_value);
-
-	TEST_ASSERT(r == 1, KVM_IOCTL_ERROR(KVM_SET_MSRS, r));
-}
-
+/*
+ * Assert on an MSR access(es) and pretty print the MSR name when possible.
+ * Note, the caller provides the stringified name so that the name of macro is
+ * printed, not the value the macro resolves to (due to macro expansion).
+ */
+#define TEST_ASSERT_MSR(cond, fmt, msr, str, args...)				\
+do {										\
+	if (__builtin_constant_p(msr)) {					\
+		TEST_ASSERT(cond, fmt, str, args);				\
+	} else if (!(cond)) {							\
+		char buf[16];							\
+										\
+		snprintf(buf, sizeof(buf), "MSR 0x%x", msr);			\
+		TEST_ASSERT(cond, fmt, buf, args);				\
+	}									\
+} while (0)
+
+#define vcpu_set_msr(vcpu, msr, val)							\
+do {											\
+	uint64_t v = val;								\
+											\
+	TEST_ASSERT_MSR(_vcpu_set_msr(vcpu, msr, v) == 1,				\
+			"KVM_SET_MSRS failed on %s, value = 0x%lx", msr, #msr, v);	\
+} while (0)
 
 void kvm_get_cpu_address_width(unsigned int *pa_bits, unsigned int *va_bits);
 bool vm_is_unrestricted_guest(struct kvm_vm *vm);