linux-kernel - Re: [PATCH] Revert "MIPS: Remove race window in page fault handling"

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Message-ID: <1417616416.10198.12.camel@lnxlarper.se.axis.com>
Date:	Wed, 3 Dec 2014 15:20:16 +0100
From:	Lars Persson <lars.persson@...s.com>
To:	Ralf Baechle <ralf@...ux-mips.org>
CC:	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>,
	"linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>,
	"james.hogan@...tec.com" <james.hogan@...tec.com>,
	"keescook@...omium.org" <keescook@...omium.org>,
	"paul.burton@...tec.com" <paul.burton@...tec.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"manuel.lauss@...il.com" <manuel.lauss@...il.com>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"blogic@...nwrt.org" <blogic@...nwrt.org>,
	"markos.chandras@...tec.com" <markos.chandras@...tec.com>
Subject: Re: [PATCH] Revert "MIPS: Remove race window in page fault handling"

Ralf

I remember now that we have applied to our tree the proposed patch
titled "MIPS HIGHMEM fixes for cache aliasing and non-DMA I/O".

This patch changes the semantics of flush_dcache_page() by using
page_mapped() instead of mapping_mapped() to decide if the flush should
be lazy. Is it this change that makes us get lazy flushes for code
mappings and therefore exposing the problem ? The ARM port which has
made a similar change to set_pte_at() also uses page_mapped() to decide
if lazy flushing is possible.

If this is true, then upstream might not need my patch. 

- Lars



On ons, 2014-12-03 at 14:42 +0100, Ralf Baechle wrote:
> Lars,
> 
> normally set_pte_at() is invoked in a 
> 
>   cache_flush_*()
>   set_pte_at()
>   tlb_flush_*()
> 
> sequence.  So I'm wondering if you're trying to fix something in set_pte_at
> that actually ought to be fixed in the cache_flush_*() function.
> 
> I'm wondering, have you identified which cache flush function in particular
> was used in the sequence in your particular bug's case?
> 
>   Ralf



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