linux-kernel - Re: [PATCH v3 3/3] PCI/MSI: Convert pci_msi_ignore

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Message-ID: <Z-O2bwbYFvOzZw0t@macbook.local>
Date: Wed, 26 Mar 2025 09:10:23 +0100
From: Roger Pau Monné <roger.pau@...rix.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Daniel Gomez <da.gomez@...nel.org>,
	Jürgen Groß <jgross@...e.com>,
	Bjorn Helgaas <helgaas@...nel.org>, linux-kernel@...r.kernel.org,
	xen-devel@...ts.xenproject.org, linux-pci@...r.kernel.org,
	Bjorn Helgaas <bhelgaas@...gle.com>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v3 3/3] PCI/MSI: Convert pci_msi_ignore_mask to per MSI
 domain flag

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....
> 
> 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.
> 
> Untested patch below.

As I'm getting reports of other people hitting this issue, is there
anything that needs to be done from my side to get the fix into
linux-next?

Thanks, Roger.