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

[Roger Pau Monnà <roger.pau@xxxxxxxxxx>]

El 22/01/15 a les 16.18, Elena Ufimtseva ha escrit:
> 
> ----- JBeulich@xxxxxxxx wrote:
> 
>>>>> On 22.01.15 at 12:37, <roger.pau@xxxxxxxxxx> wrote:
>>> El 22/01/15 a les 12.09, Jan Beulich ha escrit:
>>>>>>> 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.
>>>
>>> According to Linux IOMMU support document RMRRs reference regions
>> marked
>>> as "reserved" in the e820 memory map:
>>>
>>> https://www.kernel.org/doc/Documentation/Intel-IOMMU.txt 
>>
>> Exactly. And MMIO PCI BARs in particular are never to be
>> reflected in the E820 (not the least because they're relocatable).
>>
>>> I don't think we are setting proper IOMMU entries for this regions
>> at
>>> all with the current PVH Dom0 code. IMHO instead of just adding
>> IOMMU
>>> entries for every MMIO region we should just add IOMMU entries for
>> the
>>> RMRR regions.
>>
>> Yes, RMRR regions should certainly be put there as r/w entries.
>>
>> Jan
> 
> How it will help in cases like this when this regions are not reported as 
> RMRRs in ACPI?

AFAIK even if they are properly reported as RMRRs they won't have the
right IOMMU mappings, are you sure they are not reported as RMRRs?

Roger.


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