Re: [Xen-devel] Re: IOMMU faults

[Tim Deegan <Tim.Deegan@xxxxxxxxxx>]

Hi, 

At 11:28 +0100 on 16 Jun (1308223697), Jean Guyader wrote:
> > 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.

I think that's more or less a consensus then, that we should try to
stop the device from the IOMMU fault handler.

Looking at your patch in a bit more detail, I see two things that worry
me.  The first is that the new pci_reset_device() function does nothing
at all if the device isn't one of the particular graphics cards it know
about!

The second is this comment: 

> +    /* Leave CMD MEMORY set otherwise the platform can crashe during FLR */
> +    pci_conf_write16(bus, d, f, PCI_COMMAND, 2);

which implies that my current approach of just disabling the card might
have pretty bad conequences.  Can you expand on that?  Would it be
better just to mask out PCI_COMMAND_MASTER?  And if I do that do I need
to try and issue a reset as well (i.e. are there cards that are known to
ignore this bit?)

Cheers,

Tim.

-- 
Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Xen Platform Team
Citrix Systems UK Ltd.  (Company #02937203, SL9 0BG)

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