Re: [PATCH] exec/rom_reset: Free rom data during inmigrate skip

[Peter Maydell]

On Fri, 13 Mar 2020 at 13:21, Peter Maydell <address@hidden> wrote:
>
> On Fri, 13 Mar 2020 at 12:31, Dr. David Alan Gilbert (git)
> <address@hidden> wrote:
> >
> > From: "Dr. David Alan Gilbert" <address@hidden>
> >
> > 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 <address@hidden>
> > ---
> >  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.

thanks
-- PMM