[PATCH v9 09/13] KVM: selftests: set KVM_MEM_GUEST_MEMFD in vm_mem_add() if guest_memfd != -1

[Nikita Kalyazin]

On 15/01/2026 19:39, Ackerley Tng wrote:
> "Kalyazin, Nikita" <kalyazin at amazon.co.uk> writes:
> 
>> From: Patrick Roy <patrick.roy at 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 at linux.dev>
>> Signed-off-by: Nikita Kalyazin <kalyazin at 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 8279b6ced8d2..56ddbca91850 100644
>> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
>> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
>> @@ -1057,21 +1057,25 @@ 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) {
> 
> Might 0 turn out to be a valid return from dup() for a guest_memfd?

Yes, you're right, it isn't impossible.  Thanks!

> 
>> +             flags |= KVM_MEM_GUEST_MEMFD;
>>
>>                region->region.guest_memfd = guest_memfd;
>>                region->region.guest_memfd_offset = guest_memfd_offset;
> 
> Refactoring vm_mem_add() (/* FIXME: This thing needs to be ripped apart
> and rewritten. */) should probably be a separate patch series, but I'd
> like to take this opportunity to ask: Sean, what do you have in mind for
> the rewritten version?
> 
> Would it be something like struct vm_shape, where there are default
> mem_shapes, and the shapes get validated and then passed to
> vm_mem_add()?
> 
>> --
>> 2.50.1