Alex,Thank you very much for all these useful informations. Really appreciate 
it.Cheers 


Sent from Yahoo Mail for iPhone


On Sunday, July 12, 2020, 8:19 PM, Alex Williamson 
<alex.l.william...@gmail.com> wrote:

On Sun, Jul 12, 2020 at 6:36 PM Yv Lin <yvl...@gmail.com> wrote:

After more thoughts, I guess that 1) normally ppl don't enable vIOMMU unless 
they need to use a nested guest, as vIOMMU is slow and the memory accounting 
issue you just mentioned.

vIOMMU w/ device assignment is more often used for DPDK in a guest than for 
nested guests. 
2) host IOMMU driver actually can do io page fault and on-demanding 
pinning/mapping for ATS/PRI-capable device, but currently qemu doesn't tell if 
a pass-through device and host IOMMU can do it or not. If this is true, maybe 
we can remove the pinning of all guest memory for this type of device??

To some extent this is under development with the work Intel and others are 
contributing for SVA and SIOV support.  The primary focus is to support nested 
paging with PASID support, there are page fault interfaces proposed.  Thanks,
Alex 


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