[PATCH v2 1/2] KVM: selftests: Introduce a selftest to measure execution performance

[David Matlack <dmatlack@google.com>]

Introduce a new selftest, execute_perf_test, that uses the
perf_test_util framework to measure the performance of executing code
within a VM. This test is similar to the other perf_test_util-based
tests in that it spins up a variable number of vCPUs and runs them
concurrently, accessing memory.

In order to support executiong, extend perf_test_util to populate guest
memory with return instructions rather than random garbage. This way
memory can be execute simply by calling it.

Currently only x86-64 supports execution, but other architectures can be
easily added by providing their return code instruction.

Signed-off-by: David Matlack <dmatlack@google.com>
---
 tools/testing/selftests/kvm/.gitignore        |   1 +
 tools/testing/selftests/kvm/Makefile          |   1 +
 .../testing/selftests/kvm/execute_perf_test.c | 185 ++++++++++++++++++
 .../selftests/kvm/include/perf_test_util.h    |   2 +
 .../selftests/kvm/lib/perf_test_util.c        |  25 ++-
 5 files changed, 212 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/kvm/execute_perf_test.c

diff --git a/tools/testing/selftests/kvm/.gitignore b/tools/testing/selftests/kvm/.gitignore
index 2f0d705db9db..60ec1f0b70b5 100644
--- a/tools/testing/selftests/kvm/.gitignore
+++ b/tools/testing/selftests/kvm/.gitignore
@@ -68,6 +68,7 @@
 /demand_paging_test
 /dirty_log_test
 /dirty_log_perf_test
+/execute_perf_test
 /hardware_disable_test
 /kvm_create_max_vcpus
 /kvm_page_table_test
diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index 0172eb6cb6ee..73ea068f90de 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -132,6 +132,7 @@ TEST_GEN_PROGS_x86_64 += access_tracking_perf_test
 TEST_GEN_PROGS_x86_64 += demand_paging_test
 TEST_GEN_PROGS_x86_64 += dirty_log_test
 TEST_GEN_PROGS_x86_64 += dirty_log_perf_test
+TEST_GEN_PROGS_x86_64 += execute_perf_test
 TEST_GEN_PROGS_x86_64 += hardware_disable_test
 TEST_GEN_PROGS_x86_64 += kvm_create_max_vcpus
 TEST_GEN_PROGS_x86_64 += kvm_page_table_test
diff --git a/tools/testing/selftests/kvm/execute_perf_test.c b/tools/testing/selftests/kvm/execute_perf_test.c
new file mode 100644
index 000000000000..665bdbe62206
--- /dev/null
+++ b/tools/testing/selftests/kvm/execute_perf_test.c
@@ -0,0 +1,185 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <inttypes.h>
+#include <limits.h>
+#include <pthread.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#include "kvm_util.h"
+#include "test_util.h"
+#include "perf_test_util.h"
+#include "guest_modes.h"
+
+/* Global variable used to synchronize all of the vCPU threads. */
+static int iteration;
+
+/* Set to true when vCPU threads should exit. */
+static bool done;
+
+/* The iteration that was last completed by each vCPU. */
+static int vcpu_last_completed_iteration[KVM_MAX_VCPUS];
+
+/* Whether to overlap the regions of memory vCPUs access. */
+static bool overlap_memory_access;
+
+struct test_params {
+	/* The backing source for the region of memory. */
+	enum vm_mem_backing_src_type backing_src;
+
+	/* The amount of memory to allocate for each vCPU. */
+	uint64_t vcpu_memory_bytes;
+
+	/* The number of vCPUs to create in the VM. */
+	int nr_vcpus;
+};
+
+static void assert_ucall(struct kvm_vcpu *vcpu, uint64_t expected_ucall)
+{
+	struct ucall uc;
+
+	TEST_ASSERT(expected_ucall == get_ucall(vcpu, &uc),
+		    "Guest exited unexpectedly (expected ucall %" PRIu64
+		    ", got %" PRIu64 ")",
+		    expected_ucall, uc.cmd);
+}
+
+static bool spin_wait_for_next_iteration(int *current_iteration)
+{
+	int last_iteration = *current_iteration;
+
+	do {
+		if (READ_ONCE(done))
+			return false;
+
+		*current_iteration = READ_ONCE(iteration);
+	} while (last_iteration == *current_iteration);
+
+	return true;
+}
+
+static void vcpu_thread_main(struct perf_test_vcpu_args *vcpu_args)
+{
+	struct kvm_vcpu *vcpu = vcpu_args->vcpu;
+	int current_iteration = 0;
+
+	while (spin_wait_for_next_iteration(&current_iteration)) {
+		vcpu_run(vcpu);
+		assert_ucall(vcpu, UCALL_SYNC);
+		vcpu_last_completed_iteration[vcpu->id] = current_iteration;
+	}
+}
+
+static void spin_wait_for_vcpu(struct kvm_vcpu *vcpu, int target_iteration)
+{
+	while (READ_ONCE(vcpu_last_completed_iteration[vcpu->id]) !=
+	       target_iteration) {
+		continue;
+	}
+}
+
+static void run_iteration(struct kvm_vm *vm, const char *description)
+{
+	struct timespec ts_elapsed;
+	struct timespec ts_start;
+	struct kvm_vcpu *vcpu;
+	int next_iteration;
+
+	/* Kick off the vCPUs by incrementing iteration. */
+	next_iteration = ++iteration;
+
+	clock_gettime(CLOCK_MONOTONIC, &ts_start);
+
+	/* Wait for all vCPUs to finish the iteration. */
+	list_for_each_entry(vcpu, &vm->vcpus, list)
+		spin_wait_for_vcpu(vcpu, next_iteration);
+
+	ts_elapsed = timespec_elapsed(ts_start);
+	pr_info("%-30s: %ld.%09lds\n",
+		description, ts_elapsed.tv_sec, ts_elapsed.tv_nsec);
+}
+
+static void run_test(enum vm_guest_mode mode, void *arg)
+{
+	struct test_params *params = arg;
+	struct kvm_vm *vm;
+
+	vm = perf_test_create_vm(mode, params->nr_vcpus,
+				 params->vcpu_memory_bytes, 1,
+				 params->backing_src, !overlap_memory_access);
+
+	perf_test_start_vcpu_threads(params->nr_vcpus, vcpu_thread_main);
+
+	pr_info("\n");
+
+	perf_test_set_wr_fract(vm, 1);
+	run_iteration(vm, "Populating memory");
+
+	perf_test_set_execute(vm, true);
+	run_iteration(vm, "Executing from memory");
+
+	/* Set done to signal the vCPU threads to exit */
+	done = true;
+
+	perf_test_join_vcpu_threads(params->nr_vcpus);
+	perf_test_destroy_vm(vm);
+}
+
+static void help(char *name)
+{
+	puts("");
+	printf("usage: %s [-h] [-m mode] [-b vcpu_bytes] [-v nr_vcpus] [-o]  [-s mem_type]\n",
+	       name);
+	puts("");
+	printf(" -h: Display this help message.");
+	guest_modes_help();
+	printf(" -b: specify the size of the memory region which should be\n"
+	       "     dirtied 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");
+	backing_src_help("-s");
+	puts("");
+	exit(0);
+}
+
+int main(int argc, char *argv[])
+{
+	struct test_params params = {
+		.backing_src = DEFAULT_VM_MEM_SRC,
+		.vcpu_memory_bytes = DEFAULT_PER_VCPU_MEM_SIZE,
+		.nr_vcpus = 1,
+	};
+	int opt;
+
+	guest_modes_append_default();
+
+	while ((opt = getopt(argc, argv, "hm:b:v:os:")) != -1) {
+		switch (opt) {
+		case 'm':
+			guest_modes_cmdline(optarg);
+			break;
+		case 'b':
+			params.vcpu_memory_bytes = parse_size(optarg);
+			break;
+		case 'v':
+			params.nr_vcpus = atoi(optarg);
+			break;
+		case 'o':
+			overlap_memory_access = true;
+			break;
+		case 's':
+			params.backing_src = parse_backing_src_type(optarg);
+			break;
+		case 'h':
+		default:
+			help(argv[0]);
+			break;
+		}
+	}
+
+	for_each_guest_mode(run_test, &params);
+
+	return 0;
+}
diff --git a/tools/testing/selftests/kvm/include/perf_test_util.h b/tools/testing/selftests/kvm/include/perf_test_util.h
index eaa88df0555a..ec2540e36906 100644
--- a/tools/testing/selftests/kvm/include/perf_test_util.h
+++ b/tools/testing/selftests/kvm/include/perf_test_util.h
@@ -36,6 +36,7 @@ struct perf_test_args {
 	uint64_t size;
 	uint64_t guest_page_size;
 	int wr_fract;
+	bool execute;
 
 	/* Run vCPUs in L2 instead of L1, if the architecture supports it. */
 	bool nested;
@@ -52,6 +53,7 @@ struct kvm_vm *perf_test_create_vm(enum vm_guest_mode mode, int nr_vcpus,
 void perf_test_destroy_vm(struct kvm_vm *vm);
 
 void perf_test_set_wr_fract(struct kvm_vm *vm, int wr_fract);
+void perf_test_set_execute(struct kvm_vm *vm, bool execute);
 
 void perf_test_start_vcpu_threads(int vcpus, void (*vcpu_fn)(struct perf_test_vcpu_args *));
 void perf_test_join_vcpu_threads(int vcpus);
diff --git a/tools/testing/selftests/kvm/lib/perf_test_util.c b/tools/testing/selftests/kvm/lib/perf_test_util.c
index 9618b37c66f7..99721076d31f 100644
--- a/tools/testing/selftests/kvm/lib/perf_test_util.c
+++ b/tools/testing/selftests/kvm/lib/perf_test_util.c
@@ -38,6 +38,16 @@ static bool all_vcpu_threads_running;
 
 static struct kvm_vcpu *vcpus[KVM_MAX_VCPUS];
 
+/*
+ * When writing to guest memory, write the opcode for the `ret` instruction so
+ * that subsequent iteractions can exercise instruction fetch by calling the
+ * memory.
+ *
+ * NOTE: Non-x86 architectures would to use different values here to support
+ * execute.
+ */
+#define RETURN_OPCODE 0xC3
+
 /*
  * Continuously write to the first 8 bytes of each page in the
  * specified region.
@@ -60,8 +70,10 @@ void perf_test_guest_code(uint32_t vcpu_idx)
 		for (i = 0; i < pages; i++) {
 			uint64_t addr = gva + (i * pta->guest_page_size);
 
-			if (i % pta->wr_fract == 0)
-				*(uint64_t *)addr = 0x0123456789ABCDEF;
+			if (pta->execute)
+				((void (*)(void)) addr)();
+			else if (i % pta->wr_fract == 0)
+				*(uint64_t *)addr = RETURN_OPCODE;
 			else
 				READ_ONCE(*(uint64_t *)addr);
 		}
@@ -240,6 +252,15 @@ void __weak perf_test_setup_nested(struct kvm_vm *vm, int nr_vcpus, struct kvm_v
 	exit(KSFT_SKIP);
 }
 
+void perf_test_set_execute(struct kvm_vm *vm, bool execute)
+{
+#ifndef __x86_64__
+	TEST_ASSERT(false, "Execute not supported on this architure; see RETURN_OPCODE.");
+#endif
+	perf_test_args.execute = execute;
+	sync_global_to_guest(vm, perf_test_args);
+}
+
 static void *vcpu_thread_main(void *data)
 {
 	struct vcpu_thread *vcpu = data;
-- 
2.38.0.413.g74048e4d9e-goog