KVM: selftests: add shared hugetlbfs backing source type

This lets us run the demand paging test on top of a shared
hugetlbfs-backed area. The "shared" is key, as this allows us to
exercise userfaultfd minor faults on hugetlbfs.
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Message-Id: <20210519200339.829146-11-axelrasmussen@google.com>
Reviewed-by: Ben Gardon <bgardon@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/demand_paging_test.c

@@ -484,8 +484,10 @@ int main(int argc, char *argv[])
 		}
 	}
 
-	TEST_ASSERT(p.uffd_mode != UFFDIO_REGISTER_MODE_MINOR || p.src_type == VM_MEM_SRC_SHMEM,
-		    "userfaultfd MINOR mode requires shared memory; pick a different -t");
+	if (p.uffd_mode == UFFDIO_REGISTER_MODE_MINOR &&
+	    !backing_src_is_shared(p.src_type)) {
+		TEST_FAIL("userfaultfd MINOR mode requires shared memory; pick a different -t");
+	}
 
 	for_each_guest_mode(run_test, &p);
 

tools/testing/selftests/kvm/include/test_util.h

@@ -17,6 +17,7 @@
 #include <errno.h>
 #include <unistd.h>
 #include <fcntl.h>
+#include <sys/mman.h>
 #include "kselftest.h"
 
 static inline int _no_printf(const char *format, ...) { return 0; }
@@ -85,6 +86,7 @@ enum vm_mem_backing_src_type {
 	VM_MEM_SRC_ANONYMOUS_HUGETLB_2GB,
 	VM_MEM_SRC_ANONYMOUS_HUGETLB_16GB,
 	VM_MEM_SRC_SHMEM,
+	VM_MEM_SRC_SHARED_HUGETLB,
 	NUM_SRC_TYPES,
 };
 
@@ -101,4 +103,13 @@ size_t get_backing_src_pagesz(uint32_t i);
 void backing_src_help(void);
 enum vm_mem_backing_src_type parse_backing_src_type(const char *type_name);
 
+/*
+ * Whether or not the given source type is shared memory (as opposed to
+ * anonymous).
+ */
+static inline bool backing_src_is_shared(enum vm_mem_backing_src_type t)
+{
+	return vm_mem_backing_src_alias(t)->flag & MAP_SHARED;
+}
+
 #endif /* SELFTEST_KVM_TEST_UTIL_H */

tools/testing/selftests/kvm/lib/kvm_util.c

@@ -848,8 +848,13 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm,
 		region->mmap_size += alignment;
 
 	region->fd = -1;
-	if (src_type == VM_MEM_SRC_SHMEM) {
-		region->fd = memfd_create("kvm_selftest", MFD_CLOEXEC);
+	if (backing_src_is_shared(src_type)) {
+		int memfd_flags = MFD_CLOEXEC;
+
+		if (src_type == VM_MEM_SRC_SHARED_HUGETLB)
+			memfd_flags |= MFD_HUGETLB;
+
+		region->fd = memfd_create("kvm_selftest", memfd_flags);
 		TEST_ASSERT(region->fd != -1,
 			    "memfd_create failed, errno: %i", errno);
 

tools/testing/selftests/kvm/lib/test_util.c

@@ -240,6 +240,16 @@ const struct vm_mem_backing_src_alias *vm_mem_backing_src_alias(uint32_t i)
 			.name = "shmem",
 			.flag = MAP_SHARED,
 		},
+		[VM_MEM_SRC_SHARED_HUGETLB] = {
+			.name = "shared_hugetlb",
+			/*
+			 * No MAP_HUGETLB, we use MFD_HUGETLB instead. Since
+			 * we're using "file backed" memory, we need to specify
+			 * this when the FD is created, not when the area is
+			 * mapped.
+			 */
+			.flag = MAP_SHARED,
+		},
 	};
 	_Static_assert(ARRAY_SIZE(aliases) == NUM_SRC_TYPES,
 		       "Missing new backing src types?");
@@ -262,6 +272,7 @@ size_t get_backing_src_pagesz(uint32_t i)
 	case VM_MEM_SRC_ANONYMOUS_THP:
 		return get_trans_hugepagesz();
 	case VM_MEM_SRC_ANONYMOUS_HUGETLB:
+	case VM_MEM_SRC_SHARED_HUGETLB:
 		return get_def_hugetlb_pagesz();
 	default:
 		return MAP_HUGE_PAGE_SIZE(flag);