KVM: selftests: Add option to overlap vCPU memory access

Add an option to overlap the ranges of memory each vCPU accesses instead
of partitioning them. This option will increase the probability of
multiple vCPUs faulting on the same page at the same time, and causing
interesting races, if there are bugs in the page fault handler or
elsewhere in the kernel.

Reviewed-by: Jacob Xu <jacobhxu@google.com>
Reviewed-by: Makarand Sonare <makarandsonare@google.com>

Signed-off-by: Ben Gardon <bgardon@google.com>
Message-Id: <20210112214253.463999-6-bgardon@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 25 insertions, 7 deletions

diff --git a/tools/testing/selftests/kvm/demand_paging_test.c b/tools/testing/selftests/kvm/demand_paging_test.c
index a1cd234e6f5e..e8fda95f8389 100644
--- a/tools/testing/selftests/kvm/demand_paging_test.c
+++ b/tools/testing/selftests/kvm/demand_paging_test.c
@@ -250,6 +250,7 @@ static int setup_demand_paging(struct kvm_vm *vm,
 struct test_params {
 	bool use_uffd;
 	useconds_t uffd_delay;
+	bool partition_vcpu_memory_access;
 };
 
 static void run_test(enum vm_guest_mode mode, void *arg)
@@ -277,7 +278,8 @@ static void run_test(enum vm_guest_mode mode, void *arg)
 	vcpu_threads = malloc(nr_vcpus * sizeof(*vcpu_threads));
 	TEST_ASSERT(vcpu_threads, "Memory allocation failed");
 
-	perf_test_setup_vcpus(vm, nr_vcpus, guest_percpu_mem_size);
+	perf_test_setup_vcpus(vm, nr_vcpus, guest_percpu_mem_size,
+			      p->partition_vcpu_memory_access);
 
 	if (p->use_uffd) {
 		uffd_handler_threads =
@@ -293,10 +295,19 @@ static void run_test(enum vm_guest_mode mode, void *arg)
 		for (vcpu_id = 0; vcpu_id < nr_vcpus; vcpu_id++) {
 			vm_paddr_t vcpu_gpa;
 			void *vcpu_hva;
+			uint64_t vcpu_mem_size;
 
-			vcpu_gpa = guest_test_phys_mem + (vcpu_id * guest_percpu_mem_size);
+
+			if (p->partition_vcpu_memory_access) {
+				vcpu_gpa = guest_test_phys_mem +
+					   (vcpu_id * guest_percpu_mem_size);
+				vcpu_mem_size = guest_percpu_mem_size;
+			} else {
+				vcpu_gpa = guest_test_phys_mem;
+				vcpu_mem_size = guest_percpu_mem_size * nr_vcpus;
+			}
 			PER_VCPU_DEBUG("Added VCPU %d with test mem gpa [%lx, %lx)\n",
-				       vcpu_id, vcpu_gpa, vcpu_gpa + guest_percpu_mem_size);
+				       vcpu_id, vcpu_gpa, vcpu_gpa + vcpu_mem_size);
 
 			/* Cache the HVA pointer of the region */
 			vcpu_hva = addr_gpa2hva(vm, vcpu_gpa);
@@ -313,7 +324,7 @@ static void run_test(enum vm_guest_mode mode, void *arg)
 						&uffd_handler_threads[vcpu_id],
 						pipefds[vcpu_id * 2],
 						p->uffd_delay, &uffd_args[vcpu_id],
-						vcpu_hva, guest_percpu_mem_size);
+						vcpu_hva, vcpu_mem_size);
 			if (r < 0)
 				exit(-r);
 		}
@@ -376,7 +387,7 @@ static void help(char *name)
 {
 	puts("");
 	printf("usage: %s [-h] [-m mode] [-u] [-d uffd_delay_usec]\n"
-	       "          [-b memory] [-v vcpus]\n", name);
+	       "          [-b memory] [-v vcpus] [-o]\n", name);
 	guest_modes_help();
 	printf(" -u: use User Fault FD to handle vCPU page\n"
 	       "     faults.\n");
@@ -387,6 +398,8 @@ static void help(char *name)
 	       "     demand paged by each vCPU. e.g. 10M or 3G.\n"
 	       "     Default: 1G\n");
 	printf(" -v: specify the number of vCPUs to run.\n");
+	printf(" -o: Overlap guest memory accesses instead of partitioning\n"
+	       "     them into a separate region of memory for each vCPU.\n");
 	puts("");
 	exit(0);
 }
@@ -394,12 +407,14 @@ static void help(char *name)
 int main(int argc, char *argv[])
 {
 	int max_vcpus = kvm_check_cap(KVM_CAP_MAX_VCPUS);
-	struct test_params p = {};
+	struct test_params p = {
+		.partition_vcpu_memory_access = true,
+	};
 	int opt;
 
 	guest_modes_append_default();
 
-	while ((opt = getopt(argc, argv, "hm:ud:b:v:")) != -1) {
+	while ((opt = getopt(argc, argv, "hm:ud:b:v:o")) != -1) {
 		switch (opt) {
 		case 'm':
 			guest_modes_cmdline(optarg);
@@ -419,6 +434,9 @@ int main(int argc, char *argv[])
 			TEST_ASSERT(nr_vcpus > 0 && nr_vcpus <= max_vcpus,
 				    "Invalid number of vcpus, must be between 1 and %d", max_vcpus);
 			break;
+		case 'o':
+			p.partition_vcpu_memory_access = false;
+			break;
 		case 'h':
 		default:
 			help(argv[0]);