KVM: selftests: Use error codes to signal errors in PMU event filter test

Use '0' to signal success and '-errno' to signal failure in the PMU event
filter test so that the values are slightly less magical/arbitrary.  Using
'0' in the error paths is especially confusing as understanding it's an
error value requires following the breadcrumbs to the host code that
ultimately consumes the value.

Arguably there should also be a #define for "success", but 0/-errno is a
common enough pattern that defining another macro on top would likely do
more harm than good.

Link: https://lore.kernel.org/r/20230407233254.957013-5-seanjc@google.com
Reviewed by: Aaron Lewis <aaronlewis@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

tools/testing/selftests/kvm/x86_64/pmu_event_filter_test.c

@@ -77,7 +77,7 @@ static const uint64_t event_list[] = {
  */
 static void guest_gp_handler(struct ex_regs *regs)
 {
-	GUEST_SYNC(0);
+	GUEST_SYNC(-EFAULT);
 }
 
 /*
@@ -92,12 +92,12 @@ static void check_msr(uint32_t msr, uint64_t bits_to_flip)
 
 	wrmsr(msr, v);
 	if (rdmsr(msr) != v)
-		GUEST_SYNC(0);
+		GUEST_SYNC(-EIO);
 
 	v ^= bits_to_flip;
 	wrmsr(msr, v);
 	if (rdmsr(msr) != v)
-		GUEST_SYNC(0);
+		GUEST_SYNC(-EIO);
 }
 
 static uint64_t run_and_measure_loop(uint32_t msr_base)
@@ -114,7 +114,7 @@ static void intel_guest_code(void)
 	check_msr(MSR_CORE_PERF_GLOBAL_CTRL, 1);
 	check_msr(MSR_P6_EVNTSEL0, 0xffff);
 	check_msr(MSR_IA32_PMC0, 0xffff);
-	GUEST_SYNC(1);
+	GUEST_SYNC(0);
 
 	for (;;) {
 		uint64_t count;
@@ -138,7 +138,7 @@ static void amd_guest_code(void)
 {
 	check_msr(MSR_K7_EVNTSEL0, 0xffff);
 	check_msr(MSR_K7_PERFCTR0, 0xffff);
-	GUEST_SYNC(1);
+	GUEST_SYNC(0);
 
 	for (;;) {
 		uint64_t count;
@@ -178,13 +178,13 @@ static uint64_t run_vcpu_to_sync(struct kvm_vcpu *vcpu)
  */
 static bool sanity_check_pmu(struct kvm_vcpu *vcpu)
 {
-	bool success;
+	uint64_t r;
 
 	vm_install_exception_handler(vcpu->vm, GP_VECTOR, guest_gp_handler);
-	success = run_vcpu_to_sync(vcpu);
+	r = run_vcpu_to_sync(vcpu);
 	vm_install_exception_handler(vcpu->vm, GP_VECTOR, NULL);
 
-	return success;
+	return !r;
 }
 
 static struct kvm_pmu_event_filter *alloc_pmu_event_filter(uint32_t nevents)