Messages in this thread | | | Date | Fri, 20 Oct 2006 08:49:35 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [PATCH 1/3] Fix COW D-cache aliasing on fork |
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On Sat, 21 Oct 2006, Nick Piggin wrote: > > So moving the flush_cache_mm below the copy_page_range, to just > before the flush_tlb_mm, would work then? This would make the > race much smaller than with this patchset. > > But doesn't that still leave a race? > > What if another thread writes to cache after we have flushed it > but before flushing the TLBs? Although we've marked the the ptes > readonly, the CPU won't trap if the TLB is valid? There must be > some special way for the arch to handle this, but I can't see it.
Why not do the cache flush _after_ the TLB flush? There's still a mapping, and never mind that it's read-only: the _mapping_ still exists, and I doubt any CPU will not do the writeback (the readonly bit had better affect the _frontend_ of the memory pipeline, but affectign the back end would be insane and very hard, since you can't raise a fault any more).
Hmm?
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