Re: [RFC][PATCH 06/13] xen:vtd: create RMRR mapping

["Tian, Kevin" <kevin.tian@intel.com>]

> From: Tim Deegan [mailto:tim@xen.org]
> Sent: Thursday, April 16, 2015 11:16 PM
> 
> Hi,
> 
> At 17:21 +0800 on 10 Apr (1428686517), Tiejun Chen wrote:
> > RMRR reserved regions must be setup in the pfn space with an identity
> > mapping to reported mfn. However existing code has problem to setup
> > correct mapping when VT-d shares EPT page table, so lead to problem
> > when assigning devices (e.g GPU) with RMRR reported. This patch
> > aims to setup identity mapping in p2m layer, regardless of whether EPT
> > is shared or not.
> 
> This leaves the IOMMU mapping in place even if the p2m mapping
> fails.
> 
> I think it would be better to keep the p2m as the
> canonical mapping and make the iommu tables match the p2m.
> So, this function should not call intel_iommu_map_page() itself;
> rather, set_identity_p2m_entry() should call intel_iommu_map_page() if
> it adds the p2m entry.
> 
> Likewise for the unmap code just above this: we should be calling a
> p2m function here (guest_physmap_remove_page(), I think), which will
> then call iommu_unmap_page() for us.
> 
> Cheers,
> 
> Tim.
> 

Thanks for suggestion. It looks like a right direction.

Thanks
Kevin