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Re: [PATCH v2 2/2] xen/vpci: allow unaligned accesses by the hardware domain
- To: Roger Pau Monne <roger@xxxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 7 Aug 2026 08:39:58 +0200
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- Cc: Anthony PERARD <anthony.perard@xxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, Stewart Hildebrand <stewart.hildebrand@xxxxxxx>, Jason Andryuk <jason.andryuk@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Fri, 07 Aug 2026 06:40:11 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 06.08.2026 17:26, Roger Pau Monne wrote:
> It's possible for domains to generate unaligned PCI config space accesses
> when using ECAM, and hence vPCI should support those at least for the
> hardware domain. Such unaligned accesses to the PCI config space have been
> reported to come from ACPI logic.
>
> Relax the checking in vpci_access_allowed() to allow such accesses for the
> hardware domain, and fix the handling in pci_conf_{read,write}{16,32}() to
> fulfill them using MMCFG.
>
> MMCFG regions are identity exposed to the hardware domain, and hence such
> unaligned accesses can only come as a result of the host having MMCFG in the
> first place, as otherwise MMCFG won't be exposed to the hardware domain
> either.
>
> Note that vpci_ecam_{read,write}() already refuse accesses that cross a
> device boundary unconditionally.
>
> Reported-by: Jason Andryuk <jason.andryuk@xxxxxxx>
> Signed-off-by: Roger Pau Monné <roger@xxxxxxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Albeit without the intent to override possible remaining objections by Andrew.
Jan
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