Re: [PATCH v4 09/10] vpci/msi: Free MSI resources when init_msi() fails

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, May 20, 2025 at 08:40:28AM +0200, Jan Beulich wrote:
> On 09.05.2025 11:05, Jiqian Chen wrote:
> > When init_msi() fails, the previous new changes will hide MSI
> > capability, it can't rely on vpci_deassign_device() to remove
> > all MSI related resources anymore, those resources must be
> > removed in cleanup function of MSI.
> 
> That's because vpci_deassign_device() simply isn't called anymore?
> Could do with wording along these lines then. But (also applicable
> to the previous patch) - doesn't this need to come earlier? And is
> it sufficient to simply remove the register intercepts? Don't you
> need to put in place ones dropping all writes and making all reads
> return either 0 or ~0 (covering in particular Dom0, while for DomU-s
> this may already be the case by default behavior)?

For domUs this is already the default behavior.

For dom0 I think it should be enough to hide the capability from the
linked list, but not hide all the capability related
registers.  IMO a well behaved dom0 won't try to access capabilities
disconnected from the linked list, and in general we allow dom0 access
to as much as possible.

For dom0 Xen could drop writes to the MSI(-X) enable bit, thus forcing
MSI(-X) to stay disabled.  I however don't see this as a mandatory
step for the work here.

Regards, Roger.