* [PATCH] 2.4.0-test10-pre6 TLB flush race in establish_pte
@ 2000-10-30 21:31 Steve Pratt/Austin/IBM
2000-10-30 21:39 ` Kanoj Sarcar
2000-10-31 0:30 ` Andrea Arcangeli
0 siblings, 2 replies; 7+ messages in thread
From: Steve Pratt/Austin/IBM @ 2000-10-30 21:31 UTC (permalink / raw)
To: linux-kernel; +Cc: torvalds, linux-mm
Back in April there were discussions about the race in establish_pte with
the flush_tlb before the set_pte. Many options were discussed, but due in
part to a concern about S/390 having introduced the code, no patch ever
appeared. I talked with Martin Schwidefsky of the S/390 Linux development
team and he said that:
>the establish_pte was in fact introduced because of Linux/390. We wanted
to use the special S/390 instruction ipte (invalidate page >table entry).
In the meantime we found out that we need a lot more changes to be able to
use this instruction, so we disabled it again. >Until we have a proper
patch you should revoke the establish_pte change if you found it to be
faulty. I too think there is a race >condition.
So while there may be a more elegant solution down the road, I would like
to see the simple fix put back into 2.4. Here is the patch to essential
put the code back to the way it was before the S/390 merge. Patch is
against 2.4.0-test10pre6.
--- linux/mm/memory.c Fri Oct 27 15:26:14 2000
+++ linux-2.4.0-test10patch/mm/memory.c Fri Oct 27 15:45:54 2000
@@ -781,8 +781,8 @@
*/
static inline void establish_pte(struct vm_area_struct * vma, unsigned long address, pte_t *page_table, pte_t entry)
{
- flush_tlb_page(vma, address);
set_pte(page_table, entry);
+ flush_tlb_page(vma, address);
update_mmu_cache(vma, address, entry);
}
Linux Technology Center - IBM Corporation
11400 Burnet Road
Austin, TX 78758
(512) 838-9763 EMAIL: SLPratt@US.IBM.COM
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* Re: [PATCH] 2.4.0-test10-pre6 TLB flush race in establish_pte
2000-10-30 21:31 [PATCH] 2.4.0-test10-pre6 TLB flush race in establish_pte Steve Pratt/Austin/IBM
@ 2000-10-30 21:39 ` Kanoj Sarcar
2000-10-31 0:30 ` Andrea Arcangeli
1 sibling, 0 replies; 7+ messages in thread
From: Kanoj Sarcar @ 2000-10-30 21:39 UTC (permalink / raw)
To: Steve Pratt/Austin/IBM; +Cc: linux-kernel, torvalds, linux-mm
>
> So while there may be a more elegant solution down the road, I would like
> to see the simple fix put back into 2.4. Here is the patch to essential
> put the code back to the way it was before the S/390 merge. Patch is
> against 2.4.0-test10pre6.
>
> --- linux/mm/memory.c Fri Oct 27 15:26:14 2000
> +++ linux-2.4.0-test10patch/mm/memory.c Fri Oct 27 15:45:54 2000
> @@ -781,8 +781,8 @@
> */
> static inline void establish_pte(struct vm_area_struct * vma, unsigned long address, pte_t *page_table, pte_t entry)
> {
> - flush_tlb_page(vma, address);
> set_pte(page_table, entry);
> + flush_tlb_page(vma, address);
> update_mmu_cache(vma, address, entry);
> }
>
Great, lets do it. Definitely solves one race.
Kanoj
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* Re: [PATCH] 2.4.0-test10-pre6 TLB flush race in establish_pte
2000-10-30 21:31 [PATCH] 2.4.0-test10-pre6 TLB flush race in establish_pte Steve Pratt/Austin/IBM
2000-10-30 21:39 ` Kanoj Sarcar
@ 2000-10-31 0:30 ` Andrea Arcangeli
2000-10-31 16:23 ` Steven Pratt
1 sibling, 1 reply; 7+ messages in thread
From: Andrea Arcangeli @ 2000-10-31 0:30 UTC (permalink / raw)
To: Steve Pratt/Austin/IBM; +Cc: linux-kernel, torvalds, linux-mm
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?)
You can find the old and now useless patch here:
ftp://ftp.us.kernel.org/pub/linux/kernel/people/andrea/patches/v2.4/2.4.0-test5/tlb-flush-smp-race-1
Andrea
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* Re: [PATCH] 2.4.0-test10-pre6 TLB flush race in establish_pte
2000-10-31 0:30 ` Andrea Arcangeli
@ 2000-10-31 16:23 ` Steven Pratt
2000-10-31 16:44 ` Andrea Arcangeli
0 siblings, 1 reply; 7+ messages in thread
From: Steven Pratt @ 2000-10-31 16:23 UTC (permalink / raw)
To: linux-kernel, linux-mm; +Cc: Andrea Arcangeli
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?)
>
> You can find the old and now useless patch here:
>
>ftp://ftp.us.kernel.org/pub/linux/kernel/people/andrea/patches/v2.4/2.4.0-test5/tlb-flush-smp-race-1
I stand corrected, I missed this is my searching. Hopefully this will
get in this time.
Steve
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* Re: [PATCH] 2.4.0-test10-pre6 TLB flush race in establish_pte
2000-10-31 16:23 ` Steven Pratt
@ 2000-10-31 16:44 ` Andrea Arcangeli
0 siblings, 0 replies; 7+ messages in thread
From: Andrea Arcangeli @ 2000-10-31 16:44 UTC (permalink / raw)
To: Steven Pratt; +Cc: linux-kernel, linux-mm
On Tue, Oct 31, 2000 at 10:23:12AM -0600, Steven Pratt wrote:
> I stand corrected, I missed this is my searching. [..]
Never mind, it's nearly impossible to track every single message to l-k.
It was only informational.
> [..] Hopefully this will
> get in this time.
I hope too indeed :).
Andrea
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* Re: [PATCH] 2.4.0-test10-pre6 TLB flush race in establish_pte
2000-10-31 18:42 Ulrich.Weigand
@ 2000-10-31 19:13 ` Andrea Arcangeli
0 siblings, 0 replies; 7+ messages in thread
From: Andrea Arcangeli @ 2000-10-31 19:13 UTC (permalink / raw)
To: Ulrich.Weigand; +Cc: slpratt, linux-kernel, torvalds, linux-mm
On Tue, Oct 31, 2000 at 07:42:21PM +0100, Ulrich.Weigand@de.ibm.com wrote:
> IMO you should apply Steve's patch (without any #ifdef __s390__) now.
Agreed.
Andrea
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* Re: [PATCH] 2.4.0-test10-pre6 TLB flush race in establish_pte
@ 2000-10-31 18:42 Ulrich.Weigand
2000-10-31 19:13 ` Andrea Arcangeli
0 siblings, 1 reply; 7+ messages in thread
From: Ulrich.Weigand @ 2000-10-31 18:42 UTC (permalink / raw)
To: Andrea Arcangeli; +Cc: slpratt, linux-kernel, torvalds, linux-mm
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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2000-10-30 21:31 [PATCH] 2.4.0-test10-pre6 TLB flush race in establish_pte Steve Pratt/Austin/IBM
2000-10-30 21:39 ` Kanoj Sarcar
2000-10-31 0:30 ` Andrea Arcangeli
2000-10-31 16:23 ` Steven Pratt
2000-10-31 16:44 ` Andrea Arcangeli
2000-10-31 18:42 Ulrich.Weigand
2000-10-31 19:13 ` Andrea Arcangeli
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