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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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


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