linux-kernel - Re: [PATCH 1/3] xen/pci: do not register devices outside of PCI segment scope

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Message-ID: <28ad828a-0a9a-4637-bf55-59de2f731537@suse.com>
Date: Mon, 13 Jan 2025 08:17:23 +0100
From: Jan Beulich <jbeulich@...e.com>
To: Roger Pau Monne <roger.pau@...rix.com>
Cc: Juergen Gross <jgross@...e.com>,
 Stefano Stabellini <sstabellini@...nel.org>,
 Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
 linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org
Subject: Re: [PATCH 1/3] xen/pci: do not register devices outside of PCI
 segment scope

On 10.01.2025 15:01, Roger Pau Monne wrote:
> The PCI segment value is limited to 16 bits, however there are buses like VMD
> that fake being part of the PCI topology by adding segment with a number
> outside the scope of the PCI firmware specification range (>= 0x10000). The
> MCFG ACPI Table "PCI Segment Group Number" field is defined as having a 16 bit
> width.
> 
> Attempting to register or manage those devices with Xen would result in errors
> at best, or overlaps with existing devices living on the truncated equivalent
> segment values.
> 
> Skip notifying Xen about those devices.

Hmm, is simply omitting the notification really all it takes? How would Xen
manage MSI / MSI-X, for example, without knowing of the device? As per the
BoF on the summit in Prague(?), I continue to think we need partial driver
logic in Xen for VMD ...

Jan