Re: [v3][PATCH 1/1] xen:vtd: missing RMRR mapping while share EPT

["Chen, Tiejun" <tiejun.chen@intel.com>]

On 2014/7/25 16:24, Zhang, Yang Z wrote:
> Jan Beulich wrote on 2014-07-25:
>>>>> On 24.07.14 at 19:12, <kevin.tian@intel.com> wrote:
>>>>> From: Chen, Tiejun
>>>> Sent: Thursday, July 24, 2014 4:00 AM
>>>>
>>>> intel_iommu_map_page() does nothing if VT-d shares EPT page table.
>>>> So rmrr_identity_mapping() never create RMRR mapping but in some
>>>> cases like some GFX drivers it still need to access RMRR.
>>>
>>> this is not accurate. as long as RMRR is reported, it's always
>>> necessary to have the identity mapping there, not just needed in
>>> SOME CASES. :-)
>>
>> Actually (as also said before) I think "in some cases" is quite correct:
>> There's no guarantee that a device will actually access the region(s)
>> an RMRR may specify for it. A particular example would be the USB case
>> where iiuc these regions are needed only until legacy mode emulation gets turned off.
>
> Yes, even for Intel GFX, the RMRR is never really accessed. So we never saw any issue even without this patch.
>

Yang,

Windows GFX driver really accesses this range now. Without this patch, 
the blue screen appears.

Tiejun