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Re: [PATCH RFC v2] vPCI: account for hidden devices
- To: Stefano Stabellini <sstabellini@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 26 May 2023 08:45:00 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Fri, 26 May 2023 06:45:23 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 25.05.2023 21:32, Stefano Stabellini wrote:
> Like I wrote, personally I am happy with whatever gets us to have the PVH
> test in gitlab-ci faster.
>
> However, on the specific problem of PCI devices used by Xen and how to
> deal with them for Dom0 PVH, I think they should be completely hidden.
> Hidden in the sense that they don't appear on the Dom0 PCI bus. If the
> hidden device is a function of a multi-function PCI device, then the
> entire multi-function PCI device should be hidden.
>
> I don't think this case is very important because devices used by Xen
> are timers, IOMMUs, UARTs,
... USB debug ports (EHCI, XHCI), ...
> all devices that typically are not multi-function,
except for the ones added. Furthermore see video_endboot() for a case
of also hiding the VGA device, which isn't unlikely to have secondary
functions (sound controllers are not uncommon). Hence ...
> so it is OK to be extra careful and remove the entire
> device from Dom0 in the odd case that the device is both multi-function
> and only partially used by Xen. This is what I would do for Xen on ARM
> too.
... at best I would see this as a non-default mode of operation. Of
course we could also play more funny games with vPCI, like surfacing
a "stub" device in place of a hidden one, so the other functions can
still be found.
Jan
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