KVM: selftests: Sync perf_test_args to guest during VM creation

Copy perf_test_args to the guest during VM creation instead of relying on
the caller to do so at their leisure.  Ideally, tests wouldn't even be
able to modify perf_test_args, i.e. they would have no motivation to do
the sync, but enforcing that is arguably a net negative for readability.

No functional change intended.

[Set wr_fract=1 by default and add helper to override it since the new
 access_tracking_perf_test needs to set it dynamically.]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: David Matlack <dmatlack@google.com>
Reviewed-by: Ben Gardon <bgardon@google.com>
Message-Id: <20211111000310.1435032-13-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/access_tracking_perf_test.c

@@ -277,8 +277,7 @@ static void run_iteration(struct kvm_vm *vm, int vcpus, const char *description)
 static void access_memory(struct kvm_vm *vm, int vcpus, enum access_type access,
 			  const char *description)
 {
-	perf_test_args.wr_fract = (access == ACCESS_READ) ? INT_MAX : 1;
-	sync_global_to_guest(vm, perf_test_args);
+	perf_test_set_wr_fract(vm, (access == ACCESS_READ) ? INT_MAX : 1);
 	iteration_work = ITERATION_ACCESS_MEMORY;
 	run_iteration(vm, vcpus, description);
 }

tools/testing/selftests/kvm/demand_paging_test.c

@@ -295,8 +295,6 @@ static void run_test(enum vm_guest_mode mode, void *arg)
 	vm = perf_test_create_vm(mode, nr_vcpus, guest_percpu_mem_size, 1,
 				 p->src_type, p->partition_vcpu_memory_access);
 
-	perf_test_args.wr_fract = 1;
-
 	demand_paging_size = get_backing_src_pagesz(p->src_type);
 
 	guest_data_prototype = malloc(demand_paging_size);
@@ -345,9 +343,6 @@ static void run_test(enum vm_guest_mode mode, void *arg)
 		}
 	}
 
-	/* Export the shared variables to the guest */
-	sync_global_to_guest(vm, perf_test_args);
-
 	pr_info("Finished creating vCPUs and starting uffd threads\n");
 
 	clock_gettime(CLOCK_MONOTONIC, &start);

tools/testing/selftests/kvm/dirty_log_perf_test.c

@@ -189,7 +189,7 @@ static void run_test(enum vm_guest_mode mode, void *arg)
 				 p->slots, p->backing_src,
 				 p->partition_vcpu_memory_access);
 
-	perf_test_args.wr_fract = p->wr_fract;
+	perf_test_set_wr_fract(vm, p->wr_fract);
 
 	guest_num_pages = (nr_vcpus * guest_percpu_mem_size) >> vm_get_page_shift(vm);
 	guest_num_pages = vm_adjust_num_guest_pages(mode, guest_num_pages);
@@ -207,8 +207,6 @@ 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");
 
-	sync_global_to_guest(vm, perf_test_args);
-
 	/* Start the iterations */
 	iteration = 0;
 	host_quit = false;

tools/testing/selftests/kvm/include/perf_test_util.h

@@ -43,4 +43,6 @@ struct kvm_vm *perf_test_create_vm(enum vm_guest_mode mode, int vcpus,
 				   bool partition_vcpu_memory_access);
 void perf_test_destroy_vm(struct kvm_vm *vm);
 
+void perf_test_set_wr_fract(struct kvm_vm *vm, int wr_fract);
+
 #endif /* SELFTEST_KVM_PERF_TEST_UTIL_H */

tools/testing/selftests/kvm/lib/perf_test_util.c

@@ -94,6 +94,9 @@ struct kvm_vm *perf_test_create_vm(enum vm_guest_mode mode, int vcpus,
 
 	pr_info("Testing guest mode: %s\n", vm_guest_mode_string(mode));
 
+	/* By default vCPUs will write to memory. */
+	pta->wr_fract = 1;
+
 	/*
 	 * Snapshot the non-huge page size.  This is used by the guest code to
 	 * access/dirty pages at the logging granularity.
@@ -157,6 +160,9 @@ struct kvm_vm *perf_test_create_vm(enum vm_guest_mode mode, int vcpus,
 
 	ucall_init(vm, NULL);
 
+	/* Export the shared variables to the guest. */
+	sync_global_to_guest(vm, perf_test_args);
+
 	return vm;
 }
 
@@ -165,3 +171,9 @@ void perf_test_destroy_vm(struct kvm_vm *vm)
 	ucall_uninit(vm);
 	kvm_vm_free(vm);
 }
+
+void perf_test_set_wr_fract(struct kvm_vm *vm, int wr_fract)
+{
+	perf_test_args.wr_fract = wr_fract;
+	sync_global_to_guest(vm, perf_test_args);
+}

tools/testing/selftests/kvm/memslot_modification_stress_test.c

@@ -108,14 +108,9 @@ static void run_test(enum vm_guest_mode mode, void *arg)
 				 VM_MEM_SRC_ANONYMOUS,
 				 p->partition_vcpu_memory_access);
 
-	perf_test_args.wr_fract = 1;
-
 	vcpu_threads = malloc(nr_vcpus * sizeof(*vcpu_threads));
 	TEST_ASSERT(vcpu_threads, "Memory allocation failed");
 
-	/* Export the shared variables to the guest */
-	sync_global_to_guest(vm, perf_test_args);
-
 	pr_info("Finished creating vCPUs\n");
 
 	for (vcpu_id = 0; vcpu_id < nr_vcpus; vcpu_id++)