Re: [Xen-devel] [PATCH v4 3/4] amd-iommu: disable iommu_hap_pt_share with AMD IOMMUs

[Roger Pau Monnà <roger.pau@xxxxxxxxxx>]

On 22/07/14 19:30, Suravee Suthikulpanit wrote:
> Roger,
> 
> I am not quite sure why you would disable "iommu_hap_pt_share" for AMD
> IOMMU. The current implementation assumes that the p2m can be shared.
> 
> Also, I feel that simply just set iommu_hap_pt_share = 0 (while still
> having several places in the AMD iommu drivers and p2m-pt.c assuming
> that it can be shared) seems a bit messy.

According to the comment in p2m.h, AMD IOMMU only supports bit 52 to bit
58 in the pte to be 0, otherwise the hw generates page faults.

If we want to support doing IO to devices behind an IOMMU from page
types different than p2m_ram_rw the p2m tables cannot be shared, because
the bits from 52 to 58 will indeed be different than 0, and will
generate page faults.

Roger.


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