[PATCH RFC v4 41/44] KVM: selftests: Update private_mem_conversions_test to mmap() guest_memfd

[Ackerley Tng <ackerleytng@google.com>]

Update the private memory conversions selftest to also test conversions
that are done "in-place" via per-guest_memfd memory attributes. In-place
conversions require the host to be able to mmap() the guest_memfd so that
the host and guest can share the same backing physical memory.

This includes several updates, that are conditioned on the system
supporting per-guest_memfd attributes (kvm_has_gmem_attributes):

1. Set up guest_memfd requesting MMAP and INIT_SHARED.

2. With in-place conversions, the host's mapping points directly to the
   guest's memory. When the guest converts a region to private, host access
   to that region is blocked. Update the test to expect a SIGBUS when
   attempting to access the host virtual address (HVA) of private memory.

3. Use vm_mem_set_memory_attributes(), which chooses how to set memory
   attributes based on whether kvm_has_gmem_attributes.

Restrict the test to using VM_MEM_SRC_SHMEM because guest_memfd's required
mmap() flags and page sizes happens to align with those of
VM_MEM_SRC_SHMEM. As long as VM_MEM_SRC_SHMEM is used for src_type,
vm_mem_add() works as intended.

Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 .../kvm/x86/private_mem_conversions_test.c         | 46 ++++++++++++++++++----
 1 file changed, 38 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c b/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c
index 47f1eb9212591..29c3c5b2f538e 100644
--- a/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c
+++ b/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c
@@ -306,9 +306,14 @@ static void handle_exit_hypercall(struct kvm_vcpu *vcpu)
 	if (do_fallocate)
 		vm_guest_mem_fallocate(vm, gpa, size, map_shared);
 
-	if (set_attributes)
-		vm_set_memory_attributes(vm, gpa, size,
-					 map_shared ? 0 : KVM_MEMORY_ATTRIBUTE_PRIVATE);
+	if (set_attributes) {
+		u64 attrs = map_shared ? 0 : KVM_MEMORY_ATTRIBUTE_PRIVATE;
+		u64 flags = kvm_has_gmem_attributes ?
+			    KVM_SET_MEMORY_ATTRIBUTES2_PRESERVE : 0;
+
+		vm_mem_set_memory_attributes(vm, gpa, size, attrs, flags);
+	}
+
 	run->hypercall.ret = 0;
 }
 
@@ -352,8 +357,20 @@ static void *__test_mem_conversions(void *__vcpu)
 				size_t nr_bytes = min_t(size_t, vm->page_size, size - i);
 				uint8_t *hva = addr_gpa2hva(vm, gpa + i);
 
-				/* In all cases, the host should observe the shared data. */
-				memcmp_h(hva, gpa + i, uc.args[3], nr_bytes);
+				/*
+				 * When using per-guest_memfd memory attributes,
+				 * i.e. in-place conversion, host accesses will
+				 * point at guest memory and should SIGBUS when
+				 * guest memory is private.  When using per-VM
+				 * attributes, i.e. separate backing for shared
+				 * vs. private, the host should always observe
+				 * the shared data.
+				 */
+				if (kvm_has_gmem_attributes &&
+				    uc.args[0] == SYNC_PRIVATE)
+					TEST_EXPECT_SIGBUS(READ_ONCE(*hva));
+				else
+					memcmp_h(hva, gpa + i, uc.args[3], nr_bytes);
 
 				/* For shared, write the new pattern to guest memory. */
 				if (uc.args[0] == SYNC_SHARED)
@@ -382,6 +399,7 @@ static void test_mem_conversions(enum vm_mem_backing_src_type src_type, uint32_t
 	const size_t slot_size = memfd_size / nr_memslots;
 	struct kvm_vcpu *vcpus[KVM_MAX_VCPUS];
 	pthread_t threads[KVM_MAX_VCPUS];
+	uint64_t gmem_flags;
 	struct kvm_vm *vm;
 	int memfd, i;
 
@@ -397,12 +415,17 @@ static void test_mem_conversions(enum vm_mem_backing_src_type src_type, uint32_t
 
 	vm_enable_cap(vm, KVM_CAP_EXIT_HYPERCALL, (1 << KVM_HC_MAP_GPA_RANGE));
 
-	memfd = vm_create_guest_memfd(vm, memfd_size, 0);
+	if (kvm_has_gmem_attributes)
+		gmem_flags = GUEST_MEMFD_FLAG_MMAP | GUEST_MEMFD_FLAG_INIT_SHARED;
+	else
+		gmem_flags = 0;
+
+	memfd = vm_create_guest_memfd(vm, memfd_size, gmem_flags);
 
 	for (i = 0; i < nr_memslots; i++)
 		vm_mem_add(vm, src_type, BASE_DATA_GPA + slot_size * i,
 			   BASE_DATA_SLOT + i, slot_size / vm->page_size,
-			   KVM_MEM_GUEST_MEMFD, memfd, slot_size * i, 0);
+			   KVM_MEM_GUEST_MEMFD, memfd, slot_size * i, gmem_flags);
 
 	for (i = 0; i < nr_vcpus; i++) {
 		uint64_t gpa =  BASE_DATA_GPA + i * per_cpu_size;
@@ -452,17 +475,24 @@ static void usage(const char *cmd)
 
 int main(int argc, char *argv[])
 {
-	enum vm_mem_backing_src_type src_type = DEFAULT_VM_MEM_SRC;
+	enum vm_mem_backing_src_type src_type;
 	uint32_t nr_memslots = 1;
 	uint32_t nr_vcpus = 1;
 	int opt;
 
 	TEST_REQUIRE(kvm_check_cap(KVM_CAP_VM_TYPES) & BIT(KVM_X86_SW_PROTECTED_VM));
 
+	src_type = kvm_has_gmem_attributes ? VM_MEM_SRC_SHMEM :
+					     DEFAULT_VM_MEM_SRC;
+
 	while ((opt = getopt(argc, argv, "hm:s:n:")) != -1) {
 		switch (opt) {
 		case 's':
 			src_type = parse_backing_src_type(optarg);
+			TEST_ASSERT(!kvm_has_gmem_attributes ||
+				    src_type == VM_MEM_SRC_SHMEM,
+				    "Testing in-place conversions, only %s mem_type supported\n",
+				    vm_mem_backing_src_alias(VM_MEM_SRC_SHMEM)->name);
 			break;
 		case 'n':
 			nr_vcpus = atoi_positive("nr_vcpus", optarg);

-- 
2.53.0.1018.g2bb0e51243-goog