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Re: [PATCH v3 5/6] x86/PCI: avoid re-evaluation of extended config space accessibility
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Thu, 29 Jan 2026 16:32:42 +0100
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
- Delivery-date: Thu, 29 Jan 2026 15:32:56 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Thu, Jan 29, 2026 at 02:10:01PM +0100, Jan Beulich wrote:
> When, during boot, we have already correctly determined availability of
> the MMCFG access method for a given bus range, there's then no need to
> invoke pci_check_extcfg() again for every of the devices. This in
> particular avoids ->ext_cfg to transiently indicate the wrong state.
>
> Switch to using Xen style on lines being touched and immediately adjacent
> ones.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
One suggestion for a further addition below.
> ---
> v3: New.
>
> --- a/xen/arch/x86/physdev.c
> +++ b/xen/arch/x86/physdev.c
> @@ -528,6 +528,8 @@ ret_t do_physdev_op(int cmd, XEN_GUEST_H
> if ( !ret )
> ret = pci_segment_iterate(info.segment, physdev_check_pci_extcfg,
> &info);
> + else if ( ret > 0 ) /* Indication of "no change". */
> + ret = 0;
>
> if ( !ret && has_vpci(currd) && (info.flags &
> XEN_PCI_MMCFG_RESERVED) )
Maybe it doesn't need to be strictly done here, but now that
pci_mmcfg_reserved() signals whether the MMCFG was already registered,
could you also restrict the register_vpci_mmcfg_handler() call to ret
== 0?
That will also simplify the logic in register_vpci_mmcfg_handler()
since we no longer need to return 0 when the region is already
registered, returning -EEXIST should be fine if the caller is
adjusted.
Thanks, Roger.
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