KVM: selftests: Remove x86's so called "MMIO warning" test

Remove x86's mmio_warning_test, as it is unnecessarily complex (there's no
reason to fork, spawn threads, initialize srand(), etc..), unnecessarily
restrictive (triggering triple fault is not unique to Intel CPUs without
unrestricted guest), and provides no meaningful coverage beyond what
basic fuzzing can achieve (running a vCPU with garbage is fuzzing's bread
and butter).

That the test has *all* of the above flaws is not coincidental, as the
code was copy+pasted almost verbatim from the syzkaller reproducer that
originally found the KVM bug (which has long since been fixed).

Cc: Michal Luczaj <mhal@rbox.co>
Link: https://groups.google.com/g/syzkaller/c/lHfau8E3SOE
Link: https://lore.kernel.org/r/20230815220030.560372-1-seanjc@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>

tools/testing/selftests/kvm/Makefile

@@ -86,7 +86,6 @@ TEST_GEN_PROGS_x86_64 += x86_64/hyperv_svm_test
 TEST_GEN_PROGS_x86_64 += x86_64/hyperv_tlb_flush
 TEST_GEN_PROGS_x86_64 += x86_64/kvm_clock_test
 TEST_GEN_PROGS_x86_64 += x86_64/kvm_pv_test
-TEST_GEN_PROGS_x86_64 += x86_64/mmio_warning_test
 TEST_GEN_PROGS_x86_64 += x86_64/monitor_mwait_test
 TEST_GEN_PROGS_x86_64 += x86_64/nested_exceptions_test
 TEST_GEN_PROGS_x86_64 += x86_64/platform_info_test

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

-/*
- * mmio_warning_test
- *
- * Copyright (C) 2019, Google LLC.
- *
- * This work is licensed under the terms of the GNU GPL, version 2.
- *
- * Test that we don't get a kernel warning when we call KVM_RUN after a
- * triple fault occurs.  To get the triple fault to occur we call KVM_RUN
- * on a VCPU that hasn't been properly setup.
- *
- */
-
-#define _GNU_SOURCE
-#include <fcntl.h>
-#include <kvm_util.h>
-#include <linux/kvm.h>
-#include <processor.h>
-#include <pthread.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <sys/ioctl.h>
-#include <sys/mman.h>
-#include <sys/stat.h>
-#include <sys/types.h>
-#include <sys/wait.h>
-#include <test_util.h>
-#include <unistd.h>
-
-#define NTHREAD 4
-#define NPROCESS 5
-
-struct thread_context {
-	int kvmcpu;
-	struct kvm_run *run;
-};
-
-void *thr(void *arg)
-{
-	struct thread_context *tc = (struct thread_context *)arg;
-	int res;
-	int kvmcpu = tc->kvmcpu;
-	struct kvm_run *run = tc->run;
-
-	res = ioctl(kvmcpu, KVM_RUN, 0);
-	pr_info("ret1=%d exit_reason=%d suberror=%d\n",
-		res, run->exit_reason, run->internal.suberror);
-
-	return 0;
-}
-
-void test(void)
-{
-	int i, kvm, kvmvm, kvmcpu;
-	pthread_t th[NTHREAD];
-	struct kvm_run *run;
-	struct thread_context tc;
-
-	kvm = open("/dev/kvm", O_RDWR);
-	TEST_ASSERT(kvm != -1, "failed to open /dev/kvm");
-	kvmvm = __kvm_ioctl(kvm, KVM_CREATE_VM, NULL);
-	TEST_ASSERT(kvmvm > 0, KVM_IOCTL_ERROR(KVM_CREATE_VM, kvmvm));
-	kvmcpu = ioctl(kvmvm, KVM_CREATE_VCPU, 0);
-	TEST_ASSERT(kvmcpu != -1, KVM_IOCTL_ERROR(KVM_CREATE_VCPU, kvmcpu));
-	run = (struct kvm_run *)mmap(0, 4096, PROT_READ|PROT_WRITE, MAP_SHARED,
-				    kvmcpu, 0);
-	tc.kvmcpu = kvmcpu;
-	tc.run = run;
-	srand(getpid());
-	for (i = 0; i < NTHREAD; i++) {
-		pthread_create(&th[i], NULL, thr, (void *)(uintptr_t)&tc);
-		usleep(rand() % 10000);
-	}
-	for (i = 0; i < NTHREAD; i++)
-		pthread_join(th[i], NULL);
-}
-
-int get_warnings_count(void)
-{
-	int warnings;
-	FILE *f;
-
-	f = popen("dmesg | grep \"WARNING:\" | wc -l", "r");
-	if (fscanf(f, "%d", &warnings) < 1)
-		warnings = 0;
-	pclose(f);
-
-	return warnings;
-}
-
-int main(void)
-{
-	int warnings_before, warnings_after;
-
-	TEST_REQUIRE(host_cpu_is_intel);
-
-	TEST_REQUIRE(!vm_is_unrestricted_guest(NULL));
-
-	warnings_before = get_warnings_count();
-
-	for (int i = 0; i < NPROCESS; ++i) {
-		int status;
-		int pid = fork();
-
-		if (pid < 0)
-			exit(1);
-		if (pid == 0) {
-			test();
-			exit(0);
-		}
-		while (waitpid(pid, &status, __WALL) != pid)
-			;
-	}
-
-	warnings_after = get_warnings_count();
-	TEST_ASSERT(warnings_before == warnings_after,
-		   "Warnings found in kernel.  Run 'dmesg' to inspect them.");
-
-	return 0;
-}