selftests: KVM: use dirty logging to check if page stats work correctly

When dirty logging is enabled, KVM splits the hugepage mapping in NPT/EPT
into the smallest 4K size after guest VM writes to it. This property could
be used to check if the page stats metrics work properly in KVM x86/mmu. At
the same time, this logic might be used the other way around: using page
stats to verify if dirty logging really splits all huge pages after guest
VM writes to all memory.

So add page stats checking in dirty logging performance selftest. In
particular, add checks in three locations:
 - just after vm is created;
 - after populating memory into vm without turning on dirty logging;
 - after guest vm writing to all memory again with dirty logging turned on.

Tested using commands:
 - ./dirty_log_perf_test -s anonymous_hugetlb_1gb
 - ./dirty_log_perf_test -s anonymous_hugetlb_2mb
 - ./dirty_log_perf_test -s anonymous_thp

Cc: Sean Christopherson <seanjc@google.com>
Cc: David Matlack <dmatlack@google.com>
Cc: Jing Zhang <jingzhangos@google.com>
Cc: Peter Xu <peterx@redhat.com>

Suggested-by: Ben Gardon <bgardon@google.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>

tools/testing/selftests/kvm/dirty_log_perf_test.c

@@ -19,6 +19,10 @@
 #include "perf_test_util.h"
 #include "guest_modes.h"
 
+#ifdef __x86_64__
+#include "processor.h"
+#endif
+
 /* How many host loops to run by default (one KVM_GET_DIRTY_LOG for each loop)*/
 #define TEST_HOST_LOOP_N		2UL
 
@@ -166,6 +170,18 @@ static void run_test(enum vm_guest_mode mode, void *arg)
 	vm = perf_test_create_vm(mode, nr_vcpus, guest_percpu_mem_size,
 				 p->slots, p->backing_src);
 
+#ifdef __x86_64__
+	/*
+	 * No vCPUs have been started yet, so KVM should not have created any
+	 * mapping at this moment.
+	 */
+	TEST_ASSERT(get_page_stats(X86_PAGE_SIZE_4K) == 0,
+		    "4K page is non zero");
+	TEST_ASSERT(get_page_stats(X86_PAGE_SIZE_2M) == 0,
+		    "2M page is non zero");
+	TEST_ASSERT(get_page_stats(X86_PAGE_SIZE_1G) == 0,
+		    "1G page is non zero");
+#endif
 	perf_test_args.wr_fract = p->wr_fract;
 
 	guest_num_pages = (nr_vcpus * guest_percpu_mem_size) >> vm_get_page_shift(vm);
@@ -211,6 +227,22 @@ static void run_test(enum vm_guest_mode mode, void *arg)
 	pr_info("Populate memory time: %ld.%.9lds\n",
 		ts_diff.tv_sec, ts_diff.tv_nsec);
 
+#ifdef __x86_64__
+	TEST_ASSERT(get_page_stats(X86_PAGE_SIZE_4K) != 0,
+		    "4K page is zero");
+	/* Ensure THP page stats is non-zero to minimize the flakiness. */
+	if (p->backing_src == VM_MEM_SRC_ANONYMOUS_THP)
+		TEST_ASSERT(get_page_stats(X86_PAGE_SIZE_2M) > 0
+			"2M page number is zero");
+	else if (p->backing_src == VM_MEM_SRC_ANONYMOUS_HUGETLB_2MB)
+		TEST_ASSERT(get_page_stats(X86_PAGE_SIZE_2M) ==
+			(guest_percpu_mem_size * nr_vcpus) >> X86_PAGE_2M_SHIFT,
+			"2M page number does not match");
+	else if (p->backing_src == VM_MEM_SRC_ANONYMOUS_HUGETLB_1GB)
+		TEST_ASSERT(get_page_stats(X86_PAGE_SIZE_1G) ==
+			(guest_percpu_mem_size * nr_vcpus) >> X86_PAGE_1G_SHIFT,
+			"1G page number does not match");
+#endif
 	/* Enable dirty logging */
 	clock_gettime(CLOCK_MONOTONIC, &start);
 	enable_dirty_logging(vm, p->slots);
@@ -256,6 +288,18 @@ static void run_test(enum vm_guest_mode mode, void *arg)
 				iteration, ts_diff.tv_sec, ts_diff.tv_nsec);
 		}
 	}
+#ifdef __x86_64__
+	/*
+	 * When vCPUs writes to all memory again with dirty logging enabled, we
+	 * should see only 4K page mappings exist in KVM mmu.
+	 */
+	TEST_ASSERT(get_page_stats(X86_PAGE_SIZE_4K) != 0,
+		    "4K page is zero after dirtying memory");
+	TEST_ASSERT(get_page_stats(X86_PAGE_SIZE_2M) == 0,
+		    "2M page is non-zero after dirtying memory");
+	TEST_ASSERT(get_page_stats(X86_PAGE_SIZE_1G) == 0,
+		    "1G page is non-zero  after dirtying memory");
+#endif
 
 	/* Disable dirty logging */
 	clock_gettime(CLOCK_MONOTONIC, &start);

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

@@ -102,6 +102,7 @@ const struct vm_mem_backing_src_alias *vm_mem_backing_src_alias(uint32_t i);
 size_t get_backing_src_pagesz(uint32_t i);
 void backing_src_help(void);
 enum vm_mem_backing_src_type parse_backing_src_type(const char *type_name);
+size_t get_page_stats(uint32_t page_level);
 
 /*
  * Whether or not the given source type is shared memory (as opposed to

tools/testing/selftests/kvm/include/x86_64/processor.h

@@ -39,6 +39,13 @@
 #define X86_CR4_SMAP		(1ul << 21)
 #define X86_CR4_PKE		(1ul << 22)
 
+#define X86_PAGE_4K_SHIFT	12
+#define X86_PAGE_4K		(1ul << X86_PAGE_4K_SHIFT)
+#define X86_PAGE_2M_SHIFT	21
+#define X86_PAGE_2M		(1ul << X86_PAGE_2M_SHIFT)
+#define X86_PAGE_1G_SHIFT	30
+#define X86_PAGE_1G		(1ul << X86_PAGE_1G_SHIFT)
+
 /* CPUID.1.ECX */
 #define CPUID_VMX		(1ul << 5)
 #define CPUID_SMX		(1ul << 6)

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

@@ -15,6 +15,13 @@
 #include "linux/kernel.h"
 
 #include "test_util.h"
+#include "processor.h"
+
+static const char * const pagestat_filepaths[] = {
+	"/sys/kernel/debug/kvm/pages_4k",
+	"/sys/kernel/debug/kvm/pages_2m",
+	"/sys/kernel/debug/kvm/pages_1g",
+};
 
 /*
  * Parses "[0-9]+[kmgt]?".
@@ -141,6 +148,28 @@ size_t get_trans_hugepagesz(void)
 	return size;
 }
 
+#ifdef __x86_64__
+size_t get_stats_from_file(const char *path)
+{
+	size_t value;
+	FILE *f;
+
+	f = fopen(path, "r");
+	TEST_ASSERT(f != NULL, "Error in opening file: %s\n", path);
+
+	fscanf(f, "%ld", &value);
+	fclose(f);
+
+	return value;
+}
+
+size_t get_page_stats(uint32_t page_level)
+{
+	TEST_ASSERT(page_level <= X86_PAGE_SIZE_1G, "page type error.");
+	return get_stats_from_file(pagestat_filepaths[page_level]);
+}
+#endif
+
 size_t get_def_hugetlb_pagesz(void)
 {
 	char buf[64];