[PATCH v11 12/16] KVM: selftests: set KVM_MEM_GUEST_MEMFD in vm_mem_add() if guest_memfd != -1

Kalyazin, Nikita
2026-03-18T16:28:31Z

From: Patrick Roy <patrick.roy@linux.dev>

Have vm_mem_add() always set KVM_MEM_GUEST_MEMFD in the memslot flags if
a guest_memfd is passed in as an argument. This eliminates the
possibility where a guest_memfd instance is passed to vm_mem_add(), but
it ends up being ignored because the flags argument does not specify
KVM_MEM_GUEST_MEMFD at the same time.

This makes it easy to support more scenarios in which no vm_mem_add() is
not passed a guest_memfd instance, but is expected to allocate one.
Currently, this only happens if guest_memfd == -1 but flags &
KVM_MEM_GUEST_MEMFD != 0, but later vm_mem_add() will gain support for
loading the test code itself into guest_memfd (via
GUEST_MEMFD_FLAG_MMAP) if requested via a special
vm_mem_backing_src_type, at which point having to make sure the src_type
and flags are in-sync becomes cumbersome.

Signed-off-by: Patrick Roy <patrick.roy@linux.dev>
Signed-off-by: Nikita Kalyazin <kalyazin@amazon.com>
---
tools/testing/selftests/kvm/lib/kvm_util.c | 24 +++++++++++++---------
1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index 1959bf556e88..5b0865683047 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -1090,21 +1090,25 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type,

region->backing_src_type = src_type;

- if (flags & KVM_MEM_GUEST_MEMFD) {
- if (guest_memfd < 0) {
+ if (guest_memfd < 0) {
+ if (flags & KVM_MEM_GUEST_MEMFD) {
uint32_t guest_memfd_flags = 0;
TEST_ASSERT(!guest_memfd_offset,
"Offset must be zero when creating new guest_memfd");
guest_memfd = vm_create_guest_memfd(vm, mem_size, guest_memfd_flags);
- } else {
- /*
- * Install a unique fd for each memslot so that the fd
- * can be closed when the region is deleted without
- * needing to track if the fd is owned by the framework
- * or by the caller.
- */
- guest_memfd = kvm_dup(guest_memfd);
}
+ } else {
+ /*
+ * Install a unique fd for each memslot so that the fd
+ * can be closed when the region is deleted without
+ * needing to track if the fd is owned by the framework
+ * or by the caller.
+ */
+ guest_memfd = kvm_dup(guest_memfd);
+ }
+
+ if (guest_memfd >= 0) {
+ flags |= KVM_MEM_GUEST_MEMFD;

region->region.guest_memfd = guest_memfd;
region->region.guest_memfd_offset = guest_memfd_offset;
--
2.50.1