Re: [Qemu-devel] [RFC v2 28/32] postcopy: Allow shared memory

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Marc-André Lureau (marcandre.lureau@gmail.com) wrote:
> Hi
> 
> On Thu, Aug 24, 2017 at 12:27 PM, Dr. David Alan Gilbert (git)
> <dgilbert@redhat.com> wrote:
> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> >
> > Now that we have the mechanisms in here, allow shared memory in a
> > postcopy.
> >
> > Note that QEMU can't tell who all the users of shared regions are
> > and thus can't tell whether all the users of the shared regions
> > have appropriate support for postcopy.  Those devices that explicitly
> > support shared memory (e.g. vhost-user) must check, but it doesn't
> > stop weirder configurations causing problems.
> >
> 
> Other users should have their own migration blocker, I guess.

Yes, the ones that know about it.
The tricky thing is you can add a shared=on to any memory object you
add; I don't know that the reason it's shared is purely because it's
used by vhost-user - for all qemu knows it could be shared with 5 other
things as well.

> > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> 
> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>

Thanks.

Dave

> 
> 
> > ---
> >  migration/postcopy-ram.c | 6 ------
> >  1 file changed, 6 deletions(-)
> >
> > diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> > index 28791cf1f1..89c3aadda1 100644
> > --- a/migration/postcopy-ram.c
> > +++ b/migration/postcopy-ram.c
> > @@ -138,12 +138,6 @@ static int test_ramblock_postcopiable(const char *block_name, void *host_addr,
> >      RAMBlock *rb = qemu_ram_block_by_name(block_name);
> >      size_t pagesize = qemu_ram_pagesize(rb);
> >
> > -    if (qemu_ram_is_shared(rb)) {
> > -        error_report("Postcopy on shared RAM (%s) is not yet supported",
> > -                     block_name);
> > -        return 1;
> > -    }
> > -
> >      if (length % pagesize) {
> >          error_report("Postcopy requires RAM blocks to be a page size multiple,"
> >                       " block %s is 0x" RAM_ADDR_FMT " bytes with a "
> > --
> > 2.13.5
> >
> >
> 
> 
> 
> -- 
> Marc-André Lureau
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK