Messages in this thread |  | | From | Ulrich.Weigand@de ... | Date | Tue, 31 Oct 2000 19:42:21 +0100 | Subject | Re: [PATCH] 2.4.0-test10-pre6 TLB flush race in establish_pte |
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Andrea Arcangeli wrote:
>>On Mon, Oct 30, 2000 at 03:31:22PM -0600, Steve Pratt/Austin/IBM wrote: >> [..] no patch ever >> appeared. [..] > >You didn't followed l-k closely enough as the strict fix was submitted two >times but it got not merged. (maybe because it had an #ifdef __s390__ that was >_necessary_ by that time?)
Unfortunately, the current code is racey even on the S/390. We originally wanted to use the IPTE instruction to flush a particular TLB entry, and this requires that the old PTE value is still present at the time IPTE is performed.
Thus we wanted to place IPTE inside flush_tlb_page, and have flush_tlb_page called before the new PTE is written. However, even with the current establish_pte routine this doesn't work, as flush_tlb_page is called from several other places *after* the PTE has been changed, so we still cannot actually use IPTE.
So, what we do now is simply flush the complete TLB in flush_tlb_page, and don't use IPTE at all. This is obviously not ideal, but at least correct. Except, that is, for the race condition in establish_pte that we now share with the other architectures :-/
IMO you should apply Steve's patch (without any #ifdef __s390__) now. However, we'd like to look further for a more general solution that would allow us to make use of IPTE again in the future. This would possibly involve something like making establish_pte architecture-specific.
Mit freundlichen Gruessen / Best Regards
Ulrich Weigand
-- Dr. Ulrich Weigand Linux for S/390 Design & Development IBM Deutschland Entwicklung GmbH, Schoenaicher Str. 220, 71032 Boeblingen Phone: +49-7031/16-3727 --- Email: Ulrich.Weigand@de.ibm.com
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