1 files changed, 111 insertions, 0 deletions
diff --git a/tools/testing/selftests/kvm/s390x/shared_zeropage_test.c b/tools/testing/selftests/kvm/s390x/shared_zeropage_test.c
new file mode 100644
index 000000000000..bba0d9a6dcc8
--- /dev/null
+++ b/tools/testing/selftests/kvm/s390x/shared_zeropage_test.c
@@ -0,0 +1,111 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Test shared zeropage handling (with/without storage keys)
+ *
+ * Copyright (C) 2024, Red Hat, Inc.
+ */
+#include <sys/mman.h>
+
+#include <linux/fs.h>
+
+#include "test_util.h"
+#include "kvm_util.h"
+#include "kselftest.h"
+#include "ucall_common.h"
+
+static void set_storage_key(void *addr, uint8_t skey)
+{
+	asm volatile("sske %0,%1" : : "d" (skey), "a" (addr));
+}
+
+static void guest_code(void)
+{
+	/* Issue some storage key instruction. */
+	set_storage_key((void *)0, 0x98);
+	GUEST_DONE();
+}
+
+/*
+ * Returns 1 if the shared zeropage is mapped, 0 if something else is mapped.
+ * Returns < 0 on error or if nothing is mapped.
+ */
+static int maps_shared_zeropage(int pagemap_fd, void *addr)
+{
+	struct page_region region;
+	struct pm_scan_arg arg = {
+		.start = (uintptr_t)addr,
+		.end = (uintptr_t)addr + 4096,
+		.vec = (uintptr_t)&region,
+		.vec_len = 1,
+		.size = sizeof(struct pm_scan_arg),
+		.category_mask = PAGE_IS_PFNZERO,
+		.category_anyof_mask = PAGE_IS_PRESENT,
+		.return_mask = PAGE_IS_PFNZERO,
+	};
+	return ioctl(pagemap_fd, PAGEMAP_SCAN, &arg);
+}
+
+int main(int argc, char *argv[])
+{
+	char *mem, *page0, *page1, *page2, tmp;
+	const size_t pagesize = getpagesize();
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+	struct ucall uc;
+	int pagemap_fd;
+
+	ksft_print_header();
+	ksft_set_plan(3);
+
+	/*
+	 * We'll use memory that is not mapped into the VM for simplicity.
+	 * Shared zeropages are enabled/disabled per-process.
+	 */
+	mem = mmap(0, 3 * pagesize, PROT_READ, MAP_PRIVATE | MAP_ANON, -1, 0);
+	TEST_ASSERT(mem != MAP_FAILED, "mmap() failed");
+
+	/* Disable THP. Ignore errors on older kernels. */
+	madvise(mem, 3 * pagesize, MADV_NOHUGEPAGE);
+
+	page0 = mem;
+	page1 = page0 + pagesize;
+	page2 = page1 + pagesize;
+
+	/* Can we even detect shared zeropages? */
+	pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
+	TEST_REQUIRE(pagemap_fd >= 0);
+
+	tmp = *page0;
+	asm volatile("" : "+r" (tmp));
+	TEST_REQUIRE(maps_shared_zeropage(pagemap_fd, page0) == 1);
+
+	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
+
+	/* Verify that we get the shared zeropage after VM creation. */
+	tmp = *page1;
+	asm volatile("" : "+r" (tmp));
+	ksft_test_result(maps_shared_zeropage(pagemap_fd, page1) == 1,
+			 "Shared zeropages should be enabled\n");
+
+	/*
+	 * Let our VM execute a storage key instruction that should
+	 * unshare all shared zeropages.
+	 */
+	vcpu_run(vcpu);
+	get_ucall(vcpu, &uc);
+	TEST_ASSERT_EQ(uc.cmd, UCALL_DONE);
+
+	/* Verify that we don't have a shared zeropage anymore. */
+	ksft_test_result(!maps_shared_zeropage(pagemap_fd, page1),
+			 "Shared zeropage should be gone\n");
+
+	/* Verify that we don't get any new shared zeropages. */
+	tmp = *page2;
+	asm volatile("" : "+r" (tmp));
+	ksft_test_result(!maps_shared_zeropage(pagemap_fd, page2),
+			 "Shared zeropages should be disabled\n");
+
+	kvm_vm_free(vm);
+
+	ksft_finished();
+}