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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.01.15 at 11:59, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 22/01/15 09:53, Jan Beulich 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.
> 
> It would appear that, in this case, it is a USB controller lacking an
> appropriate RMRR description in the ACPI tables.

No, RMRRs only reference RAM pages afaik.

Jan



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