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Re: [Xen-devel] Re: IOMMU faults

On 16/06 11:07, Tim Deegan wrote:
> Hi Jean, 

Reply below,

> At 10:47 +0100 on 16 Jun (1308221277), Jean Guyader wrote:
> > We have seed such behavior when we were testing GPU assignement especially
> > the Intel GPU. The problem is that domain destruction in Xen is 
> > assynchronous
> > and right now the pci device reset is done in dom0 with some help of the 
> > toolstack.
> > 
> > In the Intel GPU case we need to make sure that the guest memory and the 
> > are still in place while we perform to reset otherwise the device drift into
> > an unstable state.
> > 
> > There is probably other ways to do that in a cleaner way but we decided to 
> > move
> > the pci reset code into Xen, so we are sure we perform the reset while the 
> > device
> > is in a known state (functionning state).
> > 
> > Attached is the patch we have in XenClient that move the pci reset into Xen.
> Thanks, Jean.  This sounds like a good idea to me, though I'd like to
> hear Wei and Allen's opinions.
> The patch is incomplete (missing the new pci_reset.[ch] files) but I get
> the general idea.  A few questions:

Reattach the full patch.

>  - Why the special handling for one graphics device on each domain? 
>    (And if one, why not all?)

No good reason really just a limitation of the patch, we can trivially
get ride of the limitation.

>  - Why not reset when the target is dom0?  It seems like it can do no
>    harm and should protect dom0 from assigning itself an active PCI
>    card. 

Reset could be quiet expensive (couple of seconds sometimes).
We did that to avoid a double reset on domain reboot.
I agree that we should remove that, or extend the IOMMU API
so we can reassign from domU to domU without going through

> Of course, even with this patch, my original question still stands:
> should Xen do something more assertive in the IOMMU fault handler?

What we really want to achive here is to stop DMA on this device.
One way of doing it is to perform a proper PCI reset (FLR, secondary
bus reset, ...) when that happens.


Attachment: iommu-vtd-pci-reset-on-reassign
Description: Text document

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