Re: Call for GSoC internship project ideas

[Peter Xu <peterx@redhat.com>]

On Mon, Jan 05, 2026 at 04:47:22PM -0500, Stefan Hajnoczi wrote:
> Dear QEMU and KVM communities,
> QEMU will apply for the Google Summer of Code internship
> program again this year. Regular contributors can submit project
> ideas that they'd like to mentor by replying to this email by
> January 30th.

There's one idea from migration side that should be self-contained, please
evaluate if this suites for the application.

I copied Marco who might be interested on such project too at least from an
user perspective on fuzzing [1].

[1] https://lore.kernel.org/all/193e5a-681dfa80-3af-701c0f80@227192887/

Thanks,

=== Fast Snapshot Load ===

'''Summary:''' Fast loadvm process based on postcopy approach

We have two common ways to load snapshots: (1) QMP "snapshot-load", or QMP
"migrate_incoming" with a "file:" URI. The idea to be discussed here should
apply to either form of loadvm, however here we will focus on "file:"
migration only, because it should be the modern and suggested way of using
snapshots nowadays.

Load snapshot currently requires all VM data (RAM states and the rest
device states) to be loaded into the QEMU instance before VM starts.

It is not required, though, to load guest memory to start the VM. For
example, in a postcopy live migration process, QEMU uses userfaultfd to
allow VM run without all of the guest memory migrated. A similar technique
can also be used in a loadvm process to make loadvm very fast, starting the
VM almost immediately right after the loadvm command.

The idea is simple: we can start the VM right after loading device states
(but without loading the guest memory), then QEMU can start the VM. In the
background, the loadvm process should keep loading all the VM data in an
atomically way. Meanwhile, the vCPUs may from time to time access a missing
guest page. QEMU needs to trap these accesses with userfaultfd, and resolve
the page faults.

After loading all the RAM state, the whole loadvm procedure is completed.

This feature needs to depend on mapped-ram feature, which allows offsetting
into the snapshots to find whatever page being asked by the guest vCPUs at
any point in time.

This feature may not be very help in VM suspend / resume use cases, because
in those cases the VM was down previously, normally it's fine waiting for
the VM to be fully loaded. However, it might be useful in some other cases
(like, frequently loading snapshots).

'''Links:'''
* https://wiki.qemu.org/ToDo/LiveMigration#Fast_load_snapshot

'''Details:'''
* Skill level: advanced
* Language: C
* Mentor: Peter Xu <peterx@redhat.com>, peterx (on #qemu IRC)

-- 
Peter Xu