Re: [PATCH v6 23/43] KVM: selftests: Create gmem fd before "regular" fd when adding memslot

[Fuad Tabba]

On Thu, 7 May 2026 at 21:23, Ackerley Tng via B4 Relay
<devnull+ackerleytng.google.com@xxxxxxxxxx> wrote:
>
> From: Sean Christopherson <seanjc@xxxxxxxxxx>
>
> When adding a memslot associated a guest_memfd instance, create/dup the
> guest_memfd before creating the "normal" backing file.  This will allow
> dup'ing the gmem fd as the normal fd when guest_memfd supports mmap(),
> i.e. to make guest_memfd the _only_ backing source for the memslot.
>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>

Reviewed-by: Fuad Tabba <tabba@xxxxxxxxxx>

Cheers,
/fuad

> ---
>  tools/testing/selftests/kvm/lib/kvm_util.c | 45 +++++++++++++++---------------
>  1 file changed, 23 insertions(+), 22 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index 2a76eca7029d3..df73b23a4c66a 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -1054,6 +1054,29 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type,
>         if (alignment > 1)
>                 region->mmap_size += alignment;
>
> +       if (flags & KVM_MEM_GUEST_MEMFD) {
> +               if (guest_memfd < 0) {
> +                       u32 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);
> +               }
> +
> +               region->region.guest_memfd = guest_memfd;
> +               region->region.guest_memfd_offset = guest_memfd_offset;
> +       } else {
> +               region->region.guest_memfd = -1;
> +       }
> +
>         region->fd = -1;
>         if (backing_src_is_shared(src_type))
>                 region->fd = kvm_memfd_alloc(region->mmap_size,
> @@ -1083,28 +1106,6 @@ 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) {
> -                       u32 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);
> -               }
> -
> -               region->region.guest_memfd = guest_memfd;
> -               region->region.guest_memfd_offset = guest_memfd_offset;
> -       } else {
> -               region->region.guest_memfd = -1;
> -       }
> -
>         region->unused_phy_pages = sparsebit_alloc();
>         if (vm_arch_has_protected_memory(vm))
>                 region->protected_phy_pages = sparsebit_alloc();
>
> --
> 2.54.0.563.g4f69b47b94-goog
>
>