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Re: [Xen-devel] PML (Page Modification Logging) design for Xen

On 02/12/2015 08:42 PM, Tim Deegan wrote:
At 07:08 +0000 on 12 Feb (1423721283), Tian, Kevin wrote:
for general log dirty, ept_invalidate_emt is required because there is
access permission change (dirtied page becomes rw after 1st fault,
so need to change them back to ro again for the new dirty tracking
round). But for PML, there's no permission change at all (always rw),
so such behavior should be noted by general logdirty layer for better
AIUI the reason for calling ept_invalidate_emt() is to avoid having to
update a large number of EPTEs at once.  If you still need to update a
large number of EPTEs (to clear the Dirty bits), that has to me
preemptable, or else use ept_invalidate_emt().

Or have I misunderstood?
I think you are correct. We still need to use ept_invalidate_emt for clearing D-bit, unless we invent a new paging layer interface, say paging_enable_log_dirty_gfn, which explicitly enables log-dirty for single GFN, either by write protection, or clearing D-bit, in case of PML.



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