Re: [Qemu-devel] [PATCH v2 0/8] acpi: make ROMs resizeable

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

* Michael S. Tsirkin (mst@redhat.com) wrote:
> On Thu, Dec 18, 2014 at 06:49:09PM +0000, Dr. David Alan Gilbert wrote:
> > * Michael S. Tsirkin (mst@redhat.com) wrote:

> > I'm generally happy with this set for what you're using it for,
> > except that I'd like some big hairy warnings in comments
> > near the resize functions to make it clear when it's safe
> > to do it.
> 
> Really always: whenever resize callback updates all
> guest visible state.

The outgoing side worries me due to previous painful encounters
with arch_init.c's migration_dirty_pages.  It's a counter that
knows exactly how many pages it has and it gets incremented/decremented
and *must* be right otherwise the migration never ends.
It's derived from used_pages in your world, so that would change.
That's just the one that comes to mind;
A comment saying 'Don't use during an outgoing migration'
would cover that - but I'm not that confident there aren't other uses
we have to be careful of.

> > What I don't really understand is how it would work for anything mapped
> > into guest address space, how that mapping would be updated.
> > 
> > Dave
> 
> That would be a job of the resize function: it can update kvm.

Yes I guess so, I'm just not sure what the guest is going to think about it.

Dave

> 
> > > 
> > > Michael S. Tsirkin (8):
> > >   cpu: add cpu_physical_memory_clear_dirty_range_nocode
> > >   memory: add memory_region_set_size
> > >   exec: cpu_physical_memory_set/clear_dirty_range
> > >   exec: split length -> used_length/max_length
> > >   exec: qemu_ram_alloc_resizeable, qemu_ram_resize
> > >   arch_init: support resizing on incoming migration
> > >   memory: API to allocate resizeable RAM MR
> > >   acpi-build: make ROMs RAM blocks resizeable
> > > 
> > >  hw/lm32/lm32_hwsetup.h  |   3 +-
> > >  include/exec/cpu-all.h  |  12 +++--
> > >  include/exec/memory.h   |  34 +++++++++++++
> > >  include/exec/ram_addr.h |  22 +++++++--
> > >  include/hw/loader.h     |   4 +-
> > >  arch_init.c             |  28 ++++++-----
> > >  exec.c                  | 129 +++++++++++++++++++++++++++++++++++++-----------
> > >  hw/core/loader.c        |  18 +++++--
> > >  hw/i386/acpi-build.c    |  19 +++++--
> > >  memory.c                |  33 +++++++++++++
> > >  10 files changed, 242 insertions(+), 60 deletions(-)
> > > 
> > > -- 
> > > MST
> > > 
> > --
> > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK