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Re: RMRRs and Phantom Functions
- To: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Wed, 27 Apr 2022 12:50:53 +0200
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- Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Kevin Tian <kevin.tian@xxxxxxxxx>, Edwin Torok <edvin.torok@xxxxxxxxxx>
- Delivery-date: Wed, 27 Apr 2022 10:51:17 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Wed, Apr 27, 2022 at 10:17:49AM +0000, Andrew Cooper wrote:
> On 27/04/2022 09:03, Roger Pau Monne wrote:
> > On Tue, Apr 26, 2022 at 05:51:32PM +0000, Andrew Cooper wrote:
> >> Specifying pci-phantom=04:00,1 does appear to work around the faults,
> >> but it's not right, because functions 1 thru 3 aren't actually phantom.
> >>
> >> Also, I don't see any logic which actually wires up phantom functions
> >> like this to share RMRRs/IVMDs in IO contexts. The faults only
> >> disappear as a side effect of 04:00.0 and 04:00.4 being in dom0, as far
> >> as I can tell.
> > I think I'm slightly confused, so those faults only happen when the
> > devices are assigned to domains different than dom0?
> >
> > It would seem to me that functions 4 to 7 not being recognized by Xen
> > should also lead to their context entries not being setup in the dom0
> > case, and thus the faults should also happen.
>
> Functions 4 thru 7 do not exist in the system. Their config space is
> all ~0's.
Yup.
> As they appear to be non-existent, no IOMMU context is set up for them,
> hence the DMA faults when their source id is actually used.
Right, somehow I read your initial description as the faults only
happening when the devices are assigned to guest, but not when in
dom0.
Thanks, Roger.
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