Re: [PATCH] pci: make ROM memory resizable

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Apr 25, 2023 at 12:02:49AM +0300, Vladimir Sementsov-Ogievskiy wrote:
> On 24.04.23 23:45, Michael S. Tsirkin wrote:
> > On Mon, Apr 24, 2023 at 04:42:00PM -0400, Michael S. Tsirkin wrote:
> > > On Mon, Apr 24, 2023 at 11:36:47PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> > > > On migration, on target we load local ROM file. But actual ROM content
> > > > migrates through migration channel. Original ROM content from local
> > > > file doesn't matter. But when size mismatch - we have an error like
> > > > 
> > > >   Size mismatch: 0000:00:03.0/virtio-net-pci.rom: 0x40000 != 0x80000: Invalid argument
> > > > 
> > > > Let's just allow resizing of ROM memory. This way migration is not
> > > > relate on local ROM file on target node which is loaded by default but
> > > > is not actually needed.
> > > > 
> > > > Signed-off-by: Vladimir Sementsov-Ogievskiy<vsementsov@yandex-team.ru>
> > Also isn't ROM size reflected in config space etc?
> > I don't remember code that would update that on migration.
> > 
> > 
> 
> Thanks a lot for fast answers!
> 
> Hmm. I'm a newbie in these things.
> 
> But yes, I noted, that my patch helps, if, for example jump from 200K to 500K zero-filled ROM file. But if jump to 600K, migration fails with
> 
> (qemu) qemu: get_pci_config_device: Bad config data: i=0x32 read: b8 device: 0 cmask: ff wmask: f0 w1cmask:0
> qemu: Failed to load PCIDevice:config
> qemu: Failed to load virtio-net:virtio
> qemu: error while loading state for instance 0x0 of device '0000:00:03.0/virtio-net'
> qemu: load of migration failed: Invalid argument
> 
> 
> I thought, that, maybe, romfile for this device just mustn't be more than 512K where config starts. But now I think that it's exactly the problem you are saying about.
> 
> 
> I know also, that there were another step around this problem: 08b1df8ff463e72b087 "pci: add romsize property".. But it doesn't help when you already have a running instance with small ROM and want to migrate it to the node where you have corresponding local ROM file updated to new package with bigger size.
> 

set romsize on destination?

> Hmm. So, simply reuse "resizable" memory blocks doesn't help. And I need more precise reinitialization of device on load of incoming migration..
> 
> -- 
> Best regards,
> Vladimir