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

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@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

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.


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


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