Re: [RFC PATCH 0/4] mm, kvm: add guest_memfd support for uffd minor faults

[Nikita Kalyazin <kalyazin@amazon.com>]

On 17/11/2025 19:39, Peter Xu wrote:
> On Mon, Nov 17, 2025 at 05:55:46PM +0000, Nikita Kalyazin wrote:
>> In our use case, Firecracker snapshot-restore using UFFD [1], we will use
>> UFFD minor/continue to respond to guest_memfd faults in user mappings
>> primarily due to VMM accesses that are required for PV (virtio) device
>> emulation and also KVM accesses when decoding MMIO operations on x86.
> 
> I'm curious if firecracker plans to support live snapshot save.  When with
> something like ioctls_supported flags, guest-memfd can declare support for
> wr-protect support easily too, and synchronous userfaultfd wr-protect traps
> will be an efficient way to do live save.
> 
> I'm guessing it's not an immediate demand now or it would have been asked
> already supporting both MINOR and WP, but I just want to raise this
> question.  Qemu already supports live snapshot save, so it'll always be
> good gmem can also support wp at some point, but it can be done later too.

No, live snapshots haven't been on our plan so far.

> 
> Thanks,
> 
> --
> Peter Xu
>