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

>>> On 24.07.14 at 19:12, <kevin.tian@xxxxxxxxx> 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.


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