Re: [PATCH] PCI: vmd: Remove MSI-X check on child devices

[Keith Busch <kbusch@kernel.org>]

On Tue, Aug 12, 2025 at 08:27:15AM +0200, Nam Cao wrote:
> On Mon, Aug 11, 2025 at 05:46:59PM -0500, Bjorn Helgaas wrote:
> > On Mon, Aug 11, 2025 at 07:39:35AM +0200, Nam Cao wrote:
> > > Commit d7d8ab87e3e7 ("PCI: vmd: Switch to msi_create_parent_irq_domain()")
> > > added a WARN_ON sanity check that child devices support MSI-X, because VMD
> > > document says [1]:
> > > 
> > >     "Intel VMD only supports MSIx Interrupts from child devices and
> > >     therefore the BIOS must enable PCIe Hot Plug and MSIx interrups [sic]."
> > 
> > Can VMD tell the difference between an incoming MSI MWr transaction
> > and an MSI-X MWr?
> > 
> > I wonder if "MSIx" was meant to mean "VMD only supports MSI or MSI-X
> > interrupts, not INTx interrupts, from child devices"?
> 
> I don't know, sorry. I am hoping that the VMD maintainers can help us here.

The doc you linked is riddled with errors. The original vmd commit
message is more accurate: VMD domains support child devices with MSI and
MSI-x interrupts. The VMD device can't even tell the difference which
one the device is using. It just manipulates messages sent to the usual
APIC address 0xfeeXXXXX.