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

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

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

Tiejun

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