Re: [RFC PATCH 0/5] madvise MADV_DOEXEC

James Bottomley
2020-08-03T15:42:57Z

On Mon, 2020-08-03 at 10:28 -0500, Eric W. Biederman wrote:
[...]
> What is wrong with live migration between one qemu process and
> another qemu process on the same machine not work for this use case?
>
> Just reusing live migration would seem to be the simplest path of
> all, as the code is already implemented. Further if something goes
> wrong with the live migration you can fallback to the existing
> process. With exec there is no fallback if the new version does not
> properly support the handoff protocol of the old version.

Actually, could I ask this another way: the other patch set you sent to
the KVM list was to snapshot the VM to a PKRAM capsule preserved across
kexec using zero copy for extremely fast save/restore. The original
idea was to use this as part of a CRIU based snapshot, kexec to new
system, restore. However, why can't you do a local snapshot, restart
qemu, restore using the PKRAM capsule to achieve exactly the same as
MADV_DOEXEC does but using a system that's easy to reason about? It
may be slightly slower, but I think we're still talking milliseconds.

James