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Re: [PATCH v2 4/4] vPCI/DomU: really no ext-caps without extended config space
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Thu, 29 Jan 2026 10:19:52 +0100
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
- Delivery-date: Thu, 29 Jan 2026 09:20:26 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Mon, Jan 19, 2026 at 03:48:01PM +0100, Jan Beulich wrote:
> Whether to emulate accesses to the first 32 bits of extended config space
> as read-as-zero or read-as-all-ones depends on whether a device actually
> has extended config space. If it doesn't, read-as-zero isn't correct; not
> getting this right may confuse functions like Linux 6.19-rc's
> pci_ext_cfg_is_aliased().
>
> Fixes: a845b50c12f3 ("vpci/header: Emulate extended capability list for dom0")
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> --- a/xen/drivers/vpci/header.c
> +++ b/xen/drivers/vpci/header.c
> @@ -830,9 +830,14 @@ static int vpci_init_ext_capability_list
> unsigned int pos = PCI_CFG_SPACE_SIZE;
>
> if ( !is_hardware_domain(pdev->domain) )
> + {
> + if ( !pdev->ext_cfg )
> + return 0;
Don't you want to possibly put this as a top-level check, so if
there's no extended config space we avoid doing the PCI_CFG_SPACE_SIZE
read for dom0 also?
Thanks, Roger.
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