Re: [virtio-comment] Re: [PATCH v1 3/8] device-context: Define the device context fields for device migration

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

On Tue, Oct 31, 2023 at 05:42:29PM +0800, Zhu, Lingshan wrote:
> > Your answer is not relevant to this discussion at all.
> > Why?
> > Because we were discussing the schemes where registers are not used.
> > One example of that was IMS. It does not matter MSI or MSIX.
> > As explained in Intel's commit message, the key to focus for IMS is "queue memory" not some hw register like MSI or MSI-X.
> you know the device always need to know a address and the data to send a
> MSI, right?

So if virtio is to use IMS then we'll need to add interfaces to program
IMS, I think. As part of that patch - it's reasonable to assume - we will
also need to add a way to retrieve IMS so it can be migrated.

However, what this example demonstrates is that the approach taken
by this proposal to migrate control path structures - namely, by
defining a structure used just for migration - means that we will
need to come up with a migration interface each time.
And that is unfortunate.

Compare to the trap and emulate approach for config space and we don't
need a new interface, we just make each field R/W.
So I feel this is something to think about, and address.
Ideas?

-- 
MST