KVM: selftests: Add dirty logging page splitting test

Add a test for page splitting during dirty logging and for hugepage
recovery after dirty logging.

Page splitting represents non-trivial behavior, which is complicated
by MANUAL_PROTECT mode, which causes pages to be split on the first
clear, instead of when dirty logging is enabled.

Add a test which makes assertions about page counts to help define the
expected behavior of page splitting and to provide needed coverage of the
behavior. This also helps ensure that a failure in eager page splitting
is not covered up by splitting in the vCPU path.

Tested by running the test on an Intel Haswell machine w/wo
MANUAL_PROTECT.

Reviewed-by: Vipin Sharma <vipinsh@google.com>
Signed-off-by: Ben Gardon <bgardon@google.com>
Link: https://lore.kernel.org/r/20230131181820.179033-3-bgardon@google.com
[sean: let the user run without hugetlb, as suggested by Paolo]
Signed-off-by: Sean Christopherson <seanjc@google.com>

tools/testing/selftests/kvm/Makefile

@@ -61,6 +61,7 @@ TEST_PROGS_x86_64 += x86_64/nx_huge_pages_test.sh
 # Compiled test targets
 TEST_GEN_PROGS_x86_64 = x86_64/cpuid_test
 TEST_GEN_PROGS_x86_64 += x86_64/cr4_cpuid_sync_test
+TEST_GEN_PROGS_x86_64 += x86_64/dirty_log_page_splitting_test
 TEST_GEN_PROGS_x86_64 += x86_64/get_msr_index_features
 TEST_GEN_PROGS_x86_64 += x86_64/exit_on_emulation_failure_test
 TEST_GEN_PROGS_x86_64 += x86_64/fix_hypercall_test

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

@@ -0,0 +1,259 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KVM dirty logging page splitting test
+ *
+ * Based on dirty_log_perf.c
+ *
+ * Copyright (C) 2018, Red Hat, Inc.
+ * Copyright (C) 2023, Google, Inc.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <linux/bitmap.h>
+
+#include "kvm_util.h"
+#include "test_util.h"
+#include "memstress.h"
+#include "guest_modes.h"
+
+#define VCPUS		2
+#define SLOTS		2
+#define ITERATIONS	2
+
+static uint64_t guest_percpu_mem_size = DEFAULT_PER_VCPU_MEM_SIZE;
+
+static enum vm_mem_backing_src_type backing_src = VM_MEM_SRC_ANONYMOUS_HUGETLB;
+
+static u64 dirty_log_manual_caps;
+static bool host_quit;
+static int iteration;
+static int vcpu_last_completed_iteration[KVM_MAX_VCPUS];
+
+struct kvm_page_stats {
+	uint64_t pages_4k;
+	uint64_t pages_2m;
+	uint64_t pages_1g;
+	uint64_t hugepages;
+};
+
+static void get_page_stats(struct kvm_vm *vm, struct kvm_page_stats *stats, const char *stage)
+{
+	stats->pages_4k = vm_get_stat(vm, "pages_4k");
+	stats->pages_2m = vm_get_stat(vm, "pages_2m");
+	stats->pages_1g = vm_get_stat(vm, "pages_1g");
+	stats->hugepages = stats->pages_2m + stats->pages_1g;
+
+	pr_debug("\nPage stats after %s: 4K: %ld 2M: %ld 1G: %ld huge: %ld\n",
+		 stage, stats->pages_4k, stats->pages_2m, stats->pages_1g,
+		 stats->hugepages);
+}
+
+static void run_vcpu_iteration(struct kvm_vm *vm)
+{
+	int i;
+
+	iteration++;
+	for (i = 0; i < VCPUS; i++) {
+		while (READ_ONCE(vcpu_last_completed_iteration[i]) !=
+		       iteration)
+			;
+	}
+}
+
+static void vcpu_worker(struct memstress_vcpu_args *vcpu_args)
+{
+	struct kvm_vcpu *vcpu = vcpu_args->vcpu;
+	int vcpu_idx = vcpu_args->vcpu_idx;
+
+	while (!READ_ONCE(host_quit)) {
+		int current_iteration = READ_ONCE(iteration);
+
+		vcpu_run(vcpu);
+
+		ASSERT_EQ(get_ucall(vcpu, NULL), UCALL_SYNC);
+
+		vcpu_last_completed_iteration[vcpu_idx] = current_iteration;
+
+		/* Wait for the start of the next iteration to be signaled. */
+		while (current_iteration == READ_ONCE(iteration) &&
+		       READ_ONCE(iteration) >= 0 &&
+		       !READ_ONCE(host_quit))
+			;
+	}
+}
+
+static void run_test(enum vm_guest_mode mode, void *unused)
+{
+	struct kvm_vm *vm;
+	unsigned long **bitmaps;
+	uint64_t guest_num_pages;
+	uint64_t host_num_pages;
+	uint64_t pages_per_slot;
+	int i;
+	uint64_t total_4k_pages;
+	struct kvm_page_stats stats_populated;
+	struct kvm_page_stats stats_dirty_logging_enabled;
+	struct kvm_page_stats stats_dirty_pass[ITERATIONS];
+	struct kvm_page_stats stats_clear_pass[ITERATIONS];
+	struct kvm_page_stats stats_dirty_logging_disabled;
+	struct kvm_page_stats stats_repopulated;
+
+	vm = memstress_create_vm(mode, VCPUS, guest_percpu_mem_size,
+				 SLOTS, backing_src, false);
+
+	guest_num_pages = (VCPUS * guest_percpu_mem_size) >> vm->page_shift;
+	guest_num_pages = vm_adjust_num_guest_pages(mode, guest_num_pages);
+	host_num_pages = vm_num_host_pages(mode, guest_num_pages);
+	pages_per_slot = host_num_pages / SLOTS;
+
+	bitmaps = memstress_alloc_bitmaps(SLOTS, pages_per_slot);
+
+	if (dirty_log_manual_caps)
+		vm_enable_cap(vm, KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2,
+			      dirty_log_manual_caps);
+
+	/* Start the iterations */
+	iteration = -1;
+	host_quit = false;
+
+	for (i = 0; i < VCPUS; i++)
+		vcpu_last_completed_iteration[i] = -1;
+
+	memstress_start_vcpu_threads(VCPUS, vcpu_worker);
+
+	run_vcpu_iteration(vm);
+	get_page_stats(vm, &stats_populated, "populating memory");
+
+	/* Enable dirty logging */
+	memstress_enable_dirty_logging(vm, SLOTS);
+
+	get_page_stats(vm, &stats_dirty_logging_enabled, "enabling dirty logging");
+
+	while (iteration < ITERATIONS) {
+		run_vcpu_iteration(vm);
+		get_page_stats(vm, &stats_dirty_pass[iteration - 1],
+			       "dirtying memory");
+
+		memstress_get_dirty_log(vm, bitmaps, SLOTS);
+
+		if (dirty_log_manual_caps) {
+			memstress_clear_dirty_log(vm, bitmaps, SLOTS, pages_per_slot);
+
+			get_page_stats(vm, &stats_clear_pass[iteration - 1], "clearing dirty log");
+		}
+	}
+
+	/* Disable dirty logging */
+	memstress_disable_dirty_logging(vm, SLOTS);
+
+	get_page_stats(vm, &stats_dirty_logging_disabled, "disabling dirty logging");
+
+	/* Run vCPUs again to fault pages back in. */
+	run_vcpu_iteration(vm);
+	get_page_stats(vm, &stats_repopulated, "repopulating memory");
+
+	/*
+	 * Tell the vCPU threads to quit.  No need to manually check that vCPUs
+	 * have stopped running after disabling dirty logging, the join will
+	 * wait for them to exit.
+	 */
+	host_quit = true;
+	memstress_join_vcpu_threads(VCPUS);
+
+	memstress_free_bitmaps(bitmaps, SLOTS);
+	memstress_destroy_vm(vm);
+
+	/* Make assertions about the page counts. */
+	total_4k_pages = stats_populated.pages_4k;
+	total_4k_pages += stats_populated.pages_2m * 512;
+	total_4k_pages += stats_populated.pages_1g * 512 * 512;
+
+	/*
+	 * Check that all huge pages were split. Since large pages can only
+	 * exist in the data slot, and the vCPUs should have dirtied all pages
+	 * in the data slot, there should be no huge pages left after splitting.
+	 * Splitting happens at dirty log enable time without
+	 * KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 and after the first clear pass
+	 * with that capability.
+	 */
+	if (dirty_log_manual_caps) {
+		ASSERT_EQ(stats_clear_pass[0].hugepages, 0);
+		ASSERT_EQ(stats_clear_pass[0].pages_4k, total_4k_pages);
+		ASSERT_EQ(stats_dirty_logging_enabled.hugepages, stats_populated.hugepages);
+	} else {
+		ASSERT_EQ(stats_dirty_logging_enabled.hugepages, 0);
+		ASSERT_EQ(stats_dirty_logging_enabled.pages_4k, total_4k_pages);
+	}
+
+	/*
+	 * Once dirty logging is disabled and the vCPUs have touched all their
+	 * memory again, the page counts should be the same as they were
+	 * right after initial population of memory.
+	 */
+	ASSERT_EQ(stats_populated.pages_4k, stats_repopulated.pages_4k);
+	ASSERT_EQ(stats_populated.pages_2m, stats_repopulated.pages_2m);
+	ASSERT_EQ(stats_populated.pages_1g, stats_repopulated.pages_1g);
+}
+
+static void help(char *name)
+{
+	puts("");
+	printf("usage: %s [-h] [-b vcpu bytes] [-s mem type]\n",
+	       name);
+	puts("");
+	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");
+	backing_src_help("-s");
+	puts("");
+}
+
+int main(int argc, char *argv[])
+{
+	int opt;
+
+	TEST_REQUIRE(get_kvm_param_bool("eager_page_split"));
+	TEST_REQUIRE(get_kvm_param_bool("tdp_mmu"));
+
+	while ((opt = getopt(argc, argv, "b:hs:")) != -1) {
+		switch (opt) {
+		case 'b':
+			guest_percpu_mem_size = parse_size(optarg);
+			break;
+		case 'h':
+			help(argv[0]);
+			exit(0);
+		case 's':
+			backing_src = parse_backing_src_type(optarg);
+			break;
+		default:
+			help(argv[0]);
+			exit(1);
+		}
+	}
+
+	if (!is_backing_src_hugetlb(backing_src)) {
+		pr_info("This test will only work reliably with HugeTLB memory. "
+			"It can work with THP, but that is best effort.\n");
+	}
+
+	guest_modes_append_default();
+
+	dirty_log_manual_caps = 0;
+	for_each_guest_mode(run_test, NULL);
+
+	dirty_log_manual_caps =
+		kvm_check_cap(KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2);
+
+	if (dirty_log_manual_caps) {
+		dirty_log_manual_caps &= (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE |
+					  KVM_DIRTY_LOG_INITIALLY_SET);
+		for_each_guest_mode(run_test, NULL);
+	} else {
+		pr_info("Skipping testing with MANUAL_PROTECT as it is not supported");
+	}
+
+	return 0;
+}