Re: [PATCH 1/1] hw/char: imx_serial: add missing migration state

On Tue, 21 Jul 2026 at 20:01, Michael Tokarev <[email protected]> wrote:
>
> On 7/15/26 16:18, Tao Ding wrote:
> > Add ucr2 from imx_serial to vmstate, and increment the version_id.
> >
> > Migrating on sabrelite can reproduce this issue:
> > 1. Prepare the U-Boot required for sabrelite. (according to sabrelite.rst)
> > 2. Compile qemu
> >      $ mkdir build && cd build && ../configure --target-list="arm-softmmu" && make -j4
> > 3. Start sabrelite and prepare for migration
> >      $ ./build/qemu-system-arm -M sabrelite \
> >      -smp 1 -m 1G -display none -serial null -serial mon:stdio \
> >      -kernel ~/u-boot
> > 4. Enter qemu monitor after uboot. (ctrl + a + c)
> >      (qemu) stop
> >      (qemu) xp /4wx 0x021e8084
> >      021e8084: 0x00004027 0x00000784 0x00008000 0x00000a01
> >      (qemu) migrate -d file:vmstate
> >      (qemu) q
> >
> > Load the migrated vmstate, before repairing:
> >
> > $ ./build/qemu-system-arm -M sabrelite \
> >      -smp 1 -m 1G -display none -serial null -serial mon:stdio \
> >      -kernel ~/u-boot -incoming file:vmstate
> >
> > (ctrl + a + c)
> >      QEMU 11.0.50 monitor - type 'help' for more information
> >      (qemu) xp /4wx 0x021e8084
> >      021e8084: 0x00000004 0x00000784 0x00008000 0x00000a01
> >      (qemu) q
> >
> > It can be found that the data for address 0x021e8084 (register of usr2 in imx_serial of sabrelite)
> > is not the data before the migration.
> >
> > After being repaired:
> > $ ./build/qemu-system-arm -M sabrelite \
> >      -smp 1 -m 1G -display none -serial null -serial mon:stdio \
> >      -kernel ~/u-boot -incoming file:vmstate
> > (ctrl + a + c)
> >      QEMU 11.0.50 monitor - type 'help' for more information
> >      (qemu) xp /4wx 0x021e8084
> >      021e8084: 0x00004027 0x00000784 0x00008000 0x00000a01
> >
> > Signed-off-by: Tao Ding <[email protected]>
>
>
> Somehow, this grow Cc: qemu-stable@ in the final version which was
> applied as v11.1.0-rc0-68-g8833ff95eaf.  I don't think this is a
> good candidate for the stable series, since this fix changes the
> migration stream format, which is very difficult to do in the stable
> series.

On the other hand it goes from "migration doesn't work" to
"migration works" for a typical guest :-)  But I agree it's
probably better to avoid migration breaks in stable branches
unless they're fixing something really critical.

-- PMM