Re: [PATCH v3 3/3] PCI/MSI: Convert pci_msi_ignore_mask to per MSI domain flag

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

On Tue, Mar 25, 2025 at 10:20:43AM +0100, Thomas Gleixner wrote:
> On Tue, Mar 25 2025 at 09:11, Thomas Gleixner wrote:
> 
> > On Mon, Mar 24 2025 at 20:18, Roger Pau Monné wrote:
> >> On Mon, Mar 24, 2025 at 07:58:14PM +0100, Daniel Gomez wrote:
> >>> The issue is that info appears to be uninitialized. So, this worked for 
> >>> me:
> >>
> >> Indeed, irq_domain->host_data is NULL, there's no msi_domain_info.  As
> >> this is x86, I was expecting x86 ot always use
> >> x86_init_dev_msi_info(), but that doesn't seem to be the case.  I
> >> would like to better understand this.
> >
> > Indeed. On x86 this should not happen at all. On architectures, which do
> > not use (hierarchical) interrupt domains, it will return NULL.
> >
> > So I really want to understand why this happens on x86 before such a
> > "fix" is deployed.
> 
> So after staring at it some more it's clear. Without XEN, the domain
> returned is the MSI parent domain, which is the vector domain in that
> setup. That does not have a domain info set. But on legacy architectures
> there is not even a domain.
> 
> It's really wonderful that we have a gazillion ways to manage the
> backends of PCI/MSI....

I'm a bit confused by what msi_create_device_irq_domain() does, as it
does allocate an irq_domain with an associated msi_domain_info
structure, however that irq_domain is set in
dev->msi.data->__domains[domid].domain rather than dev->msi.domain,
and doesn't override the default irq_domain set by
pcibios_device_add().

And the default x86 irq_domain (set by pcibios_device_add()) doesn't
have an associated msi_domain_info.

> So none of the suggested pointer checks will cover it correctly. Though
> there is already a function which allows to query MSI domain flags
> independent of the underlying insanity. Sorry for not catching it in
> review.

Oh, that's nice, I didn't know about that helper.

> Untested patch below.

LGTM, but (as you can see) I'm not expert on that area.

Thanks, Roger.