Re: [Qemu-devel] [RFC PATCH 0/4] MSI affinity for assigned devices

[Alex Williamson]

On Wed, 2012-11-28 at 00:08 +0100, Jan Kiszka wrote:
> On 2012-11-27 23:00, Alex Williamson wrote:
> > This is post-1.3 material, so I'll just post it as an RFC for now.
> > 
> > MSI routing updates aren't currently handled by pci-assign or
> > vfio-pci (when using KVM acceleration), which means that trying to
> > set interrupt SMP affinity in the guest has no effect unless MSI is
> > completely disabled and re-enabled.  This series fixes this for both
> > device assignment backends using similar schemes.  We store the last
> > MSIMessage programmed to KVM and do updates to the MSI route when it
> > changes.  pci-assign takes a little bit of refactoring to make this
> > happen cleanly.  Thanks,
> 
> This should rather be done by implementing vector notifiers for MSI as
> well. That way the device model no longer has to track reasons for
> vector changes in an open-coded fashion, just like we already do for MSI-X.
> 
> Was on my todo list for a long time, but I never reached this item.

MSI masking is optional and not many devices seem to support it.  What I
see with a linux guest is that it just overwrites the address/data while
MSI is enabled.  What were you thinking for notifiers? mask, unmask,
update?  I'm not sure I'm interested enough in this to add MSI vector
notifiers.  Thanks,

Alex