Messages in this thread | | | Subject | Re: [RFC][PATCH 4/6] arm, mm: Convert arm to generic tlb | From | Peter Zijlstra <> | Date | Thu, 17 May 2012 18:59:19 +0200 |
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On Thu, 2012-05-17 at 18:44 +0200, Peter Zijlstra wrote: > > So the RCU code can from ppc in commit > 267239116987d64850ad2037d8e0f3071dc3b5ce, which has similar behaviour. > Also I suspect the mm_users < 2 test will be incorrect for ARM since > even the one user can be concurrent with your speculation engine. > > Right, last mail, I promise, I've confused myself enough already! :-)
OK, so ppc/sparc are special (forgot all about s390) I think by the time they are done with unmap_page_range() their hardware hash-tables are empty and nobody but software page-table walkers will still access the linux page tables.
So when we do free_pgtables() to clean up the actual page-tables. Power/Sparc need to RCU free this to allow concurrent software page-table walkers like gup_fast.
Thus I don't think they need to tlb flush again because their hardware doesn't actually walk the link page-tables, it walks hash-tables, which by this time are empty.
Now if x86/Xen were to use this, it would indeed also need to TLB flush when freeing the page-tables, since its hardware walkers do indeed traverse these pages and we need to sync against them.
So my first patch in the tlb-unify tree is actually buggy.
Humm,. what to do adding a tlb flush in there might slow down ppc/sparc unnecessarily.. dave/ben? I guess we need more knobs :-(
Now its quite possible I've utterly confused myself and everybody reading, apologies for that, I shall rest and purge all from memory and start over before commenting more..
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