KVM: selftests: Add back the missing check of MONITOR/MWAIT availability

The revamp of monitor/mwait test missed the original check of feature
availability [*]. If MONITOR/MWAIT is not supported or is disabled by
IA32_MISC_ENABLE on the host, executing MONITOR or MWAIT instruction
from guest doesn't cause monitor/mwait VM exits, but a #UD.

[*] https://lore.kernel.org/all/[email protected]/

Reported-by: Xuelian Guo <[email protected]>
Fixes: 80fd663 ("selftests: kvm: revamp MONITOR/MWAIT tests")
Signed-off-by: Chenyi Qiang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sean Christopherson <[email protected]>

Author: Qiangcy

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

@@ -74,6 +74,7 @@ int main(int argc, char *argv[])
 	int testcase;
 	char test[80];
 
+	TEST_REQUIRE(this_cpu_has(X86_FEATURE_MWAIT));
 	TEST_REQUIRE(kvm_has_cap(KVM_CAP_DISABLE_QUIRKS2));
 
 	ksft_print_header();