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

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Message-ID: <Z-KLhBHoNBB_lr7y@macbook.local>
Date: Tue, 25 Mar 2025 11:55:00 +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 11:27:51AM +0100, Thomas Gleixner wrote:
> On Tue, Mar 25 2025 at 11:22, Roger Pau Monné wrote:
> > On Tue, Mar 25, 2025 at 10:20:43AM +0100, Thomas Gleixner wrote:
> > 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().
> 
> The default irq domain is a parent domain in that case on top of which
> the per device domains are built. And those are private to the device.

Sorry to ask, but shouldn't dev_get_msi_domain() return the specific
device domain rather than the parent one?  Otherwise I feel the
function should rather be named dev_get_parent_msi_domain().

> The XEN variant uses the original global PCI/MSI domain concept with
> this outrageous domain wrapper hack. A crime committed by some tglx
> dude.

I see.  So the proper way would be for Xen to not override the default
x86 irq_domain in dev->msi.domain (so don't have a Xen PV specific
version of x86_init.irqs.create_pci_msi_domain) and instead do
something similar to what VMD does?

Thanks, Roger.