[PATCH 4/4] selftests: KVM: use dirty logging to check if page stats work correctly

[Mingwei Zhang]

When dirty logging is enabled, KVM splits the all hugepage mapping in
NPT/EPT into the smallest 4K size. This property could be used to check if
the page stats metrics work properly in KVM 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. Moreover, when dirty logging is
disabled, KVM zaps corresponding SPTEs and we could check whether the large
pages come back when guest touches the pages again.

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 but before enabling dirty logging;
 - just after turning on dirty logging.
 - after one final iteration after turning off dirty logging.

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

Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
Cc: David Matlack <dmatlack@xxxxxxxxxx>
Cc: Jing Zhang <jingzhangos@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>

Suggested-by: Ben Gardon <bgorden@xxxxxxxxxx>
Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
---
 .../selftests/kvm/dirty_log_perf_test.c       | 52 +++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/tools/testing/selftests/kvm/dirty_log_perf_test.c b/tools/testing/selftests/kvm/dirty_log_perf_test.c
index 1954b964d1cf..ab0457d91658 100644
--- a/tools/testing/selftests/kvm/dirty_log_perf_test.c
+++ b/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
 
@@ -185,6 +189,14 @@ static void run_test(enum vm_guest_mode mode, void *arg)
 				 p->slots, p->backing_src,
 				 p->partition_vcpu_memory_access);
 
+#ifdef __x86_64__
+	TEST_ASSERT(vm_get_single_stat(vm, "pages_4k") == 0,
+		    "4K page is non zero");
+	TEST_ASSERT(vm_get_single_stat(vm, "pages_2m") == 0,
+		    "2M page is non zero");
+	TEST_ASSERT(vm_get_single_stat(vm, "pages_1g") == 0,
+		    "1G page is non zero");
+#endif
 	perf_test_set_wr_fract(vm, p->wr_fract);
 
 	guest_num_pages = (nr_vcpus * guest_percpu_mem_size) >> vm_get_page_shift(vm);
@@ -222,6 +234,16 @@ 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(vm_get_single_stat(vm, "pages_4k") != 0,
+		    "4K page is zero");
+	if (p->backing_src == VM_MEM_SRC_ANONYMOUS_THP)
+		TEST_ASSERT(vm_get_single_stat(vm, "pages_2m") != 0,
+			    "2M page is zero");
+	if (p->backing_src == VM_MEM_SRC_ANONYMOUS_HUGETLB_1GB)
+		TEST_ASSERT(vm_get_single_stat(vm, "pages_1g") != 0,
+			    "1G page is zero");
+#endif
 	/* Enable dirty logging */
 	clock_gettime(CLOCK_MONOTONIC, &start);
 	enable_dirty_logging(vm, p->slots);
@@ -267,6 +289,14 @@ static void run_test(enum vm_guest_mode mode, void *arg)
 				iteration, ts_diff.tv_sec, ts_diff.tv_nsec);
 		}
 	}
+#ifdef __x86_64__
+	TEST_ASSERT(vm_get_single_stat(vm, "pages_4k") != 0,
+		    "4K page is zero after dirty logging");
+	TEST_ASSERT(vm_get_single_stat(vm, "pages_2m") == 0,
+		    "2M page is non-zero after dirty logging");
+	TEST_ASSERT(vm_get_single_stat(vm, "pages_1g") == 0,
+		    "1G page is non-zero after dirty logging");
+#endif
 
 	/* Disable dirty logging */
 	clock_gettime(CLOCK_MONOTONIC, &start);
@@ -275,6 +305,28 @@ static void run_test(enum vm_guest_mode mode, void *arg)
 	pr_info("Disabling dirty logging time: %ld.%.9lds\n",
 		ts_diff.tv_sec, ts_diff.tv_nsec);
 
+#ifdef __x86_64__
+	/*
+	 * Increment iteration to run the vcpus again to verify if huge pages
+	 * come back.
+	 */
+	iteration++;
+	pr_info("Starting the final iteration to verify page stats\n");
+
+	for (vcpu_id = 0; vcpu_id < nr_vcpus; vcpu_id++) {
+		while (READ_ONCE(vcpu_last_completed_iteration[vcpu_id])
+		       != iteration)
+			;
+	}
+
+	if (p->backing_src == VM_MEM_SRC_ANONYMOUS_THP)
+		TEST_ASSERT(vm_get_single_stat(vm, "pages_2m") != 0,
+			    "2M page is zero");
+	if (p->backing_src == VM_MEM_SRC_ANONYMOUS_HUGETLB_1GB)
+		TEST_ASSERT(vm_get_single_stat(vm, "pages_1g") != 0,
+			    "1G page is zero");
+#endif
+
 	/* Tell the vcpu thread to quit */
 	host_quit = true;
 	perf_test_join_vcpu_threads(nr_vcpus);
-- 
2.35.1.894.gb6a874cedc-goog