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Re: [Xen-devel] GPU passthrough performance regression in >4GB vms due to XSA-60 changes

On 05/19/2014 01:01 PM, Jan Beulich wrote:
On 19.05.14 at 12:42, <tomasz.wroblewski@xxxxxxxxx> wrote:
Actually seems to be like the plausible explanation for the performance
issues we see could be that

- some region of guest space has been relocated by hvmloader out to
64bit memory to enlarge pci mmio hole (which stays in 32bit space)
- BUT the caching on that relocated region is UC since at the time of
the relocation MTRR was disabled and that caused the EPT entry to get UC
But this would be easily seen from 'D' debug key output - did you
check this is what is the case?
Yes I've checked that, though I used some homebrew EPT dumping code instead. Mentioned it a bit earlier, in the original post as well as http://lists.xen.org/archives/html/xen-devel/2014-05/msg01965.html. I just incorrectly thought that it's the BAR being relocated which introduced some confusion..


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