Re: [Qemu-devel] [PATCH RFC 1/2] memory: make MemoryRegion alias migratable

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

* Igor Mammedov (imammedo@redhat.com) wrote:
> On Tue, 30 Jul 2019 15:34:54 +0200
> Paolo Bonzini <pbonzini@redhat.com> wrote:
> 
> > On 30/07/19 15:25, Igor Mammedov wrote:
> > > I'd guess you've meant RAMBlocks instead of memory regions, if that's it
> > > then yes, every alias pointing to RAM backed memory region will have
> > > RAMBlock that's points to aliased part of aliased memory region.
> > 
> > The question is just, does it break migration from old QEMU to new QEMU
> > on x86 (which has plenty of RAM-backed aliases)?  If not, explain that
> > in the commit message or in a code comment.
> 
> pc/q35 old<->new new<->old ping pong tests worked fine (qemu with default devices).
> 
> My understanding was that one needs to call vmstate_register_ram()
> to make memory region migratable, which marks specific RAMBlock
> as migratable. So just assigning new RAMBlock to mr->ram_block shouldn't
> affect migration, unless vmstate_register_ram() is called on alias.

You're right; that's actually relatively new and I forget about it.
 From Cedric's b895de50271 in 3.0, before that we migrated every
RAMBlock.

So yes, I think you should be OK.

Dave

> I'll add it to commit message.
> 
> > 
> > Paolo
> > 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK