linux-kernel - [RFC PATCH RESEND 3/3] KVM: selftests: Test guest_memfd behavior with respect to stage 2 page tables

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Message-ID: <0ec7349858142439ed0a250e6c04edf84cb0f488.1760551864.git.wyihan@google.com>
Date: Wed, 15 Oct 2025 18:58:57 +0000
From: Lisa Wang <wyihan@...gle.com>
To: linmiaohe@...wei.com, nao.horiguchi@...il.com, akpm@...ux-foundation.org, 
	pbonzini@...hat.com, shuah@...nel.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, 
	linux-kselftest@...r.kernel.org
Cc: david@...hat.com, rientjes@...gle.com, seanjc@...gle.com, 
	ackerleytng@...gle.com, vannapurve@...gle.com, michael.roth@....com, 
	jiaqiyan@...gle.com, tabba@...gle.com, dave.hansen@...ux.intel.com, 
	Lisa Wang <wyihan@...gle.com>
Subject: [RFC PATCH RESEND 3/3] KVM: selftests: Test guest_memfd behavior with
 respect to stage 2 page tables

Test that
+ memory failure handling results in unmapping of bad memory from stage
  2 page tables, hence requiring faulting on next guest access
+ when the guest tries to fault a poisoned page from guest_memfd, the
  userspace VMM informed with EHWPOISON

Co-developed-by: Ackerley Tng <ackerleytng@...gle.com>
Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
Signed-off-by: Lisa Wang <wyihan@...gle.com>
---
 .../testing/selftests/kvm/guest_memfd_test.c  | 65 +++++++++++++++++++
 1 file changed, 65 insertions(+)

diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
index 7bcf8d2d5d4d..dc3398e22edd 100644
--- a/tools/testing/selftests/kvm/guest_memfd_test.c
+++ b/tools/testing/selftests/kvm/guest_memfd_test.c
@@ -539,6 +539,70 @@ static void test_guest_memfd_guest(void)
 	kvm_vm_free(vm);
 }
 
+static void __guest_code_read(uint8_t *mem)
+{
+	READ_ONCE(*mem);
+	GUEST_DONE();
+}
+
+static void guest_read(struct kvm_vcpu *vcpu, uint64_t gpa, int expected_errno)
+{
+	vcpu_arch_set_entry_point(vcpu, __guest_code_read);
+	vcpu_args_set(vcpu, 1, gpa);
+
+	if (expected_errno) {
+		TEST_ASSERT_EQ(_vcpu_run(vcpu), -1);
+		TEST_ASSERT_EQ(errno, expected_errno);
+	} else {
+		vcpu_run(vcpu);
+		TEST_ASSERT_EQ(get_ucall(vcpu, NULL), UCALL_DONE);
+	}
+}
+
+static void test_memory_failure_guest(void)
+{
+	const uint64_t gpa = SZ_4G;
+	const int slot = 1;
+
+	unsigned long memory_failure_pfn;
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+	uint8_t *mem;
+	size_t size;
+	int fd;
+
+	if (!kvm_has_cap(KVM_CAP_GUEST_MEMFD_FLAGS))
+		return;
+
+	vm = __vm_create_shape_with_one_vcpu(VM_SHAPE_DEFAULT, &vcpu, 1, __guest_code_read);
+
+	size = vm->page_size;
+	fd = vm_create_guest_memfd(vm, size, GUEST_MEMFD_FLAG_MMAP | GUEST_MEMFD_FLAG_INIT_SHARED);
+	vm_set_user_memory_region2(vm, slot, KVM_MEM_GUEST_MEMFD, gpa, size, NULL, fd, 0);
+
+	mem = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+	TEST_ASSERT(mem != MAP_FAILED, "mmap() for guest_memfd should succeed.");
+	virt_pg_map(vm, gpa, gpa);
+
+	/* Fault in page to read pfn, then unmap page for testing. */
+	READ_ONCE(*mem);
+	memory_failure_pfn = addr_to_pfn(mem);
+	munmap(mem, size);
+
+	/* Fault page into stage2 page tables. */
+	guest_read(vcpu, gpa, 0);
+
+	mark_memory_failure(memory_failure_pfn, 0);
+
+	guest_read(vcpu, gpa, EHWPOISON);
+	munmap(mem, size);
+
+	close(fd);
+	kvm_vm_free(vm);
+
+	unmark_memory_failure(memory_failure_pfn, 0);
+}
+
 int main(int argc, char *argv[])
 {
 	unsigned long vm_types, vm_type;
@@ -559,4 +623,5 @@ int main(int argc, char *argv[])
 		test_guest_memfd(vm_type);
 
 	test_guest_memfd_guest();
+	test_memory_failure_guest();
 }
-- 
2.51.0.788.g6d19910ace-goog