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

On 2014/7/25 16:28, Zhang, Yang Z wrote:
Chen, Tiejun wrote on 2014-07-25:
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.

Okay, so for Linux guest, it works well even without having RMRR mapping.



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