On Fri, 13 Mar 2020 at 13:34, Dr. David Alan Gilbert
<dgilb...@redhat.com> wrote:
>
> * Peter Maydell (peter.mayd...@linaro.org) wrote:
> > On Fri, 13 Mar 2020 at 13:21, Peter Maydell <peter.mayd...@linaro.org>
> > wrote:
> > >
> > > On Fri, 13 Mar 2020 at 12:31, Dr. David Alan Gilbert (git)
> > > <dgilb...@redhat.com> wrote:
> > > >
> > > > From: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
> > > >
> > > > Commit 355477f8c73e9 skips rom reset when we're an incoming migration
> > > > so as not to overwrite shared ram in the ignore-shared migration
> > > > optimisation.
> > > > However, it's got an unexpected side effect that because it skips
> > > > freeing the ROM data, when rom_reset gets called later on, after
> > > > migration (e.g. during a reboot), the ROM does get reset to the original
> > > > file contents. Because of seabios/x86's weird reboot process
> > > > this confuses a reboot into hanging after a migration.
> > > >
> > > > Fixes: 355477f8c73e9 ("migration: do not rom_reset() during incoming
> > > > migration")
> > > > https://bugzilla.redhat.com/show_bug.cgi?id=1809380
> > > >
> > > > Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
> > > > ---
> > > > hw/core/loader.c | 23 ++++++++++++++---------
> > > > 1 file changed, 14 insertions(+), 9 deletions(-)
> > > >
> > >
> > > > QTAILQ_FOREACH(rom, &roms, next) {
> > > > if (rom->fw_file) {
> > > > continue;
> > > > }
> > > > + /*
> > > > + * We don't need to fill in the RAM with ROM data because
> > > > we'll fill
> > > > + * the data in during the next incoming migration in all
> > > > cases. Note
> > > > + * that some of those RAMs can actually be modified by the
> > > > guest on ARM
> > > > + * so this is probably the only right thing to do here.
> > > > + */
> > > > + if (runstate_check(RUN_STATE_INMIGRATE) && rom->data) {
> > > > + /*
> > > > + * Free it so that a rom_reset after migration doesn't
> > > > overwrite a
> > > > + * potentially modified 'rom'.
> > > > + */
> > > > + rom_free_data(rom);
> > >
> > > Shouldn't this condition match the condition in rom_reset()
> > > for when we call rom_free_data()? You want the behaviour
> > > on a subsequent reset to match the behaviour you'd get
> > > if you did a reset on the source end without the migration.
> >
> > Wait, this *is* rom_reset(). Now I'm really confused.
>
> The exsiting rom_reset gets called multiple times:
> a) During init
> This actually copies the ROMs and then calls rom_free_data
>
> b) During a subsequent reboot
> This is mostly skipped because rom->data is now free because
> of the prior call to rom_free_data during (a)
>
> During an inbound migrate, (a) happens before the migration, and
> (b) happens during a reboot after the migration.
>
> The problem is that 355477f8c73e9 caused (a) to be skipped
> then when (b) happens it actually overwrites the ROM because
> the rom_free_data had been skipped. What I'm doing here is
> doing the rom_free_data(..) which causes it to then skip this
> iteration during (a) AND causes it to skip it during (b).
OK, but why is your condition for when to call rom_free_data()
in this special case not the same as the condition that we
use in the normal no-migration-involved case? I would expect
those to match up.
thanks
-- PMM
