linux-kernel - Re: [PATCH] aio: fix D-cache aliasing issues

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Date:	Sun, 17 Nov 2013 20:15:14 -0500
From:	John David Anglin <dave.anglin@...l.net>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
CC:	Helge Deller <deller@....de>, linux-parisc@...r.kernel.org,
	Benjamin LaHaise <bcrl@...ck.org>,
	Simon Baatz <gmbnomis@...il.com>, linux-aio@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] aio: fix D-cache aliasing issues


On 17-Nov-13, at 7:52 PM, James Bottomley wrote:

>> +void flush_user_dcache_page(struct page *page);
>> +
>
> The split into flush_kernel.. and flush_user.. is pointless.  We  
> have no
> use for a flush_user_.. API because it's not part of the standard  
> linux
> one.  Plus it's going to confuse those who come after us no end  
> because
> now we're different from every other architecture.

I introduced it because it seemed to be what was needed on parisc when
we map a kernel page on PA8800/PA8900.  We need this to ensure what the
kernel sees is up to date and also to ensure that we don't create  
inequivalent
aliases between the user and kernel mappings.

>
>> #define flush_kernel_dcache_range(start,size) \
>> 	flush_kernel_dcache_range_asm((start), (start)+(size));
>> /* vmap range flushes and invalidates.  Architecturally, we don't  
>> need
>> @@ -125,18 +127,27 @@ flush_anon_page(struct vm_area_struct *vma,  
>> struct page *page, unsigned long vma
>> void mark_rodata_ro(void);
>> #endif
>>
>> -#ifdef CONFIG_PA8X00
>> -/* Only pa8800, pa8900 needs this */
>> -
>> #include <asm/kmap_types.h>
>>
>> #define ARCH_HAS_KMAP
>>
>> -void kunmap_parisc(void *addr);
>> +static inline void kmap_parisc(struct page *page)
>> +{
>> +	if (parisc_requires_coherency())
>> +		flush_user_dcache_page(page);
>> +}
>
> No ... if we're genuinely moving coherency into kmap/kunmap, this  
> has to
> become
>
> 	flush_dcache_page(page);
>
> unconditionally.

There are two things about flush_dcache_page(page):

1) The flush could be deferred.  I don't think we want that.
2) It seems to unnecessarily call flush_kernel_dcache_page().

Dave
--
John David Anglin	dave.anglin@...l.net



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