Re: [PULL 01/30] migration: Fix migration crash when target psize larger than host

[Juan Quintela]

On Fri, Feb 10, 2023, 16:01 Peter Xu <peterx@redhat.com> wrote:

On Fri, Feb 10, 2023 at 01:11:34PM +0100, Juan Quintela wrote:
> Michael Tokarev <mjt@tls.msk.ru> wrote:
> > 07.02.2023 03:56, Juan Quintela wrote:
> >> From: Peter Xu <peterx@redhat.com>
> >> Commit d9e474ea56 overlooked the case where the target psize is even
> >> larger
> >> than the host psize.  One example is Alpha has 8K page size and migration
> >> will start to crash the source QEMU when running Alpha migration on x86.
> >> Fix it by detecting that case and set host start/end just to cover
> >> the
> >> single page to be migrated.
> >
> > FWIW, commit in question, which is d9e474ea56, has been applied after the
> > last released version to date, which is 7.2.0.  So I guess this change is
> > not applicable to -stable.
>
> I think it should.
>
> This is a bug that can happen when your host page is smaller than the
> guest size.
>
> And has been that way for a long time.
> Once told that, people don't migrate alpha guests a lot, but it can also
> happens with funny combinations of large pages.
>
> Peter Xu knows more about this.

Thanks, Juan.

I think Michael was correct that d9e474ea56 is only merged after our most
recent release (which is v7.2.0).  So it doesn't need to have stable copied
(aka, it doesn't need to be applied to any QEMU's stable tree).

Juan, could you help drop the "cc: stable" line if the pull is going to
have a new version?

Sure.

I hope the problem is somewhere else.

Side note: I think in the case where we have wrongly have the cc:stable it
shouldn't hurt either, because when the stable tree tries to pick it up
it'll find it doesn't apply at all, then a downstream-only patch will be
needed, then we'll also figure all things out, just later.

Thanks,

--
Peter Xu