Re: [Xen-devel] [PATCH RFC] p2m: p2m_mmio_direct set RW permissions

[Elena Ufimtseva <elena.ufimtseva@xxxxxxxxxx>]

----- JBeulich@xxxxxxxx wrote:

> >>> On 21.01.15 at 21:55, <elena.ufimtseva@xxxxxxxxxx> wrote:
> > p2m_mmio_direct should result in setting IOMMUF_readable and
> IOMMUF_writable
> > flags.
> > When pvh domain maps mmio regions, the EPT entries are not getting
> mapped.
> > This leads to IOMMU Page faults for some devices, as for example USB
> Host
> > controllers with embedded Debug devices. See
> pvh-set-need_iommu-early RFC
> > patch discussion fgor detail.
> 
> Even more so that the two patches aren't even a series, that part
> of the description belongs here, not in the other patch.
> 
> > I will appreciate your comments and ideas in regards to this
> change.
> > 
> > Looking at Roger patches (xen/pvh: check permissions when adding
> MMIO 
> > regions)
> > the mmio memory type is proposed to be changed from p2m_mmio_direct
> to 
> > p2m_access_rw.
> > This type still does not have proper IOMMU flags mapping.
> 
> A fundamental question is what business devices have to DMA their
> own (or other devices') MMIO space. I could remotely see a need
> for this for e.g. frame buffers, but I have difficulty understanding
> this for USB devices. Please at the very least provide details on the
> MMIO regions that those devices have, and which of them you
> observed IOMMU faults on.
> 
> Jan

Hi Jan

The IOMMU Page fault addresses are 0xd5d45 and 0xd5d46 in case of ThinkCentre 
machine.
If you would like to see any other details I am happy to send them as well.

With Dell Precision it is not known what addresses do trigger page faults 
because it just hangs.

I don't have an answer why the devices need to access DMA of their MMIOs. Will 
ask linux usb folks.

Elena

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