Re: [Qemu-devel] [PATCH v4] migration: do not rom_reset() during incoming migration

[Catherine Ho <catherine.hecx@gmail.com>]

Hi Paolo
Ping, is any other comment I hadn't addressed?

Cheers
Catherine

On Thu, 6 Jun 2019 at 02:31, Dr. David Alan Gilbert <dgilbert@redhat.com>
wrote:

> Paolo, can you take this one please.
>
> * Catherine Ho (catherine.hecx@gmail.com) wrote:
> > Commit 18269069c310 ("migration: Introduce ignore-shared capability")
> > addes ignore-shared capability to bypass the shared ramblock (e,g,
> > membackend + numa node). It does good to live migration.
> >
> > As told by Yury,this commit expectes that QEMU doesn't write to guest RAM
> > until VM starts, but it does on aarch64 qemu:
> > Backtrace:
> > 1  0x000055f4a296dd84 in address_space_write_rom_internal () at
> > exec.c:3458
> > 2  0x000055f4a296de3a in address_space_write_rom () at exec.c:3479
> > 3  0x000055f4a2d519ff in rom_reset () at hw/core/loader.c:1101
> > 4  0x000055f4a2d475ec in qemu_devices_reset () at hw/core/reset.c:69
> > 5  0x000055f4a2c90a28 in qemu_system_reset () at vl.c:1675
> > 6  0x000055f4a2c9851d in main () at vl.c:4552
> >
> > Actually, on arm64 virt marchine, ramblock "dtb" will be filled into ram
> > druing rom_reset. In ignore-shared incoming case, this rom filling
> > is not required since all the data has been stored in memory backend
> > file.
> >
> > Further more, as suggested by Peter Xu, if we do rom_reset() now with
> > these ROMs then the RAM data should be re-filled again too with the
> > migration stream coming in.
> >
> > Fixes: commit 18269069c310 ("migration: Introduce ignore-shared
> > capability")
> > Suggested-by: Yury Kotov <yury-kotov@yandex-team.ru>
> > Suggested-by: Peter Xu <peterx@redhat.com>
> > Signed-off-by: Catherine Ho <catherine.hecx@gmail.com>
> > ---
> >  hw/core/loader.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/hw/core/loader.c b/hw/core/loader.c
> > index fe5cb24122..040109464b 100644
> > --- a/hw/core/loader.c
> > +++ b/hw/core/loader.c
> > @@ -1087,6 +1087,15 @@ static void rom_reset(void *unused)
> >  {
> >      Rom *rom;
> >
> > +    /*
> > +     * 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))
> > +        return;
> > +
> >      QTAILQ_FOREACH(rom, &roms, next) {
> >          if (rom->fw_file) {
> >              continue;
> > --
> > 2.17.1
> >
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>