[PATCH v2 4/5] KVM: selftests: Add wrfract to common guest code

[Ben Gardon <bgardon@xxxxxxxxxx>]

Wrfract will be used by the dirty logging perf test introduced later in
this series to dirty memory sparsely.

Signed-off-by: Ben Gardon <bgardon@xxxxxxxxxx>
---
 tools/testing/selftests/kvm/demand_paging_test.c     | 2 ++
 tools/testing/selftests/kvm/include/perf_test_util.h | 1 +
 tools/testing/selftests/kvm/lib/perf_test_util.c     | 5 ++++-
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/kvm/demand_paging_test.c b/tools/testing/selftests/kvm/demand_paging_test.c
index 63ea7c06e1141..72b8890c0dc3b 100644
--- a/tools/testing/selftests/kvm/demand_paging_test.c
+++ b/tools/testing/selftests/kvm/demand_paging_test.c
@@ -264,6 +264,8 @@ static void run_test(enum vm_guest_mode mode, bool use_uffd,
 	int vcpu_id;
 	int r;
 
+	perf_test_args.wr_fract = 1;
+
 	vm = create_vm(mode, vcpus, vcpu_memory_bytes);
 
 	guest_data_prototype = malloc(perf_test_args.host_page_size);
diff --git a/tools/testing/selftests/kvm/include/perf_test_util.h b/tools/testing/selftests/kvm/include/perf_test_util.h
index 4d52b9ee13c42..645b942ae0229 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 {
 	struct kvm_vm *vm;
 	uint64_t host_page_size;
 	uint64_t guest_page_size;
+	int wr_fract;
 
 	struct vcpu_args vcpu_args[MAX_VCPUS];
 };
diff --git a/tools/testing/selftests/kvm/lib/perf_test_util.c b/tools/testing/selftests/kvm/lib/perf_test_util.c
index fa7efbac9ef8a..1abb6b1321c3c 100644
--- a/tools/testing/selftests/kvm/lib/perf_test_util.c
+++ b/tools/testing/selftests/kvm/lib/perf_test_util.c
@@ -44,7 +44,10 @@ void guest_code(uint32_t vcpu_id)
 	for (i = 0; i < pages; i++) {
 		uint64_t addr = gva + (i * perf_test_args.guest_page_size);
 
-		*(uint64_t *)addr = 0x0123456789ABCDEF;
+		if (i % perf_test_args.wr_fract == 0)
+			*(uint64_t *)addr = 0x0123456789ABCDEF;
+		else
+			READ_ONCE(*(uint64_t *)addr);
 	}
 
 	GUEST_SYNC(1);
-- 
2.29.1.341.ge80a0c044ae-goog