Messages in this thread | | | Date | Fri, 05 Oct 2007 12:40:05 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: race with page_referenced_one->ptep_test_and_clear_young and pagetable setup/pulldown |
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Rik van Riel wrote: > This makes for a narrow race window, during which ptep_test_and_clear_young > cannot clear the referenced bit and may end up causing a crash. We do not > care about it not clearing the referenced bit during that window, since it > will be cleared during the next go-around and the race is very rare. >
Is this the only possible case? It's just the one I found while testing under high memory pressure.
> Hence, the only thing we need to fix is the crash. > > We can do that by adding an entry for ptep_test_and_clear_young to the > exception table. This way we do not need to turn this into a new paravirt > ops hook (since the fast path is exactly the same as x86 native) and there > is no need for added complexity. > > Also, Xen would not conflict with SPLIT_PTLOCK_CPUS. >
Well, isn't the correct fix to make Xen take all the pagetable locks while pinning/unpinning? Adding exception handling to test_and_clear_bit would solve this particular race, but are there others (either now or potentially)? Seems fragile.
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