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[Xen-devel] Superpages for VT-D

I do not have a clear answer about use of super pages in VT-D for the IOMMU.


Here is from the release notes for 4.1:




Further, support for EPT/VTd 1GB/2MB super pages has been added to Xen, reducing the TLB overhead. EPT/VTd page table sharing simplifies the support for Intel’s IOMMU by allowing the CPU’s Enhanced Page Table to be directly utilized by the VTd IOMMU.



Based on this check in, I also see the output from Xen on my system showing HAP page sizes as 4kB, 2MB, and 1GB – but it does not say which one is in use.




1.       Are superpages (2MB, 1GB) enabled by default in Xen? If enabled, what size?

2.       On Intel, if superpages are enabled, is that used for the IOMMU?

3.       If it is not enabled by default, how does one enable it?




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