From: anfei <anfei.zhou@gmail.com>
To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux@arm.linux.org.uk, jamie@shareable.org
Subject: Re: cache alias in mmap + write
Date: Wed, 20 Jan 2010 17:52:42 +0800 [thread overview]
Message-ID: <20100120095242.GA5672@desktop> (raw)
In-Reply-To: <20100120174630.4071.A69D9226@jp.fujitsu.com>
On Wed, Jan 20, 2010 at 06:10:11PM +0900, KOSAKI Motohiro wrote:
> Hello,
>
> > diff --git a/mm/filemap.c b/mm/filemap.c
> > index 96ac6b0..07056fb 100644
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -2196,6 +2196,9 @@ again:
> > if (unlikely(status))
> > break;
> >
> > + if (mapping_writably_mapped(mapping))
> > + flush_dcache_page(page);
> > +
> > pagefault_disable();
> > copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
> > pagefault_enable();
>
> I'm not sure ARM cache coherency model. but I guess correct patch is here.
>
> + if (mapping_writably_mapped(mapping))
> + flush_dcache_page(page);
> +
> pagefault_disable();
> copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
> pagefault_enable();
> - flush_dcache_page(page);
>
>
> Why do we need to call flush_dcache_page() twice?
>
The latter flush_dcache_page is used to flush the kernel changes
(iov_iter_copy_from_user_atomic), which makes the userspace to see the
write, and the one I added is used to flush the userspace changes.
And I think it's better to split this function into two:
flush_dcache_user_page(page);
kmap_atomic(page);
write to page;
kunmap_atomic(page);
flush_dcache_kern_page(page);
But currently there is no such API.
>
>
>
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next prev parent reply other threads:[~2010-01-20 9:52 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-01-20 8:26 cache alias in mmap + write anfei
2010-01-20 9:10 ` KOSAKI Motohiro
2010-01-20 9:52 ` anfei [this message]
2010-01-21 1:10 ` KOSAKI Motohiro
2010-01-21 1:32 ` Jamie Lokier
2010-01-21 3:06 ` anfei zhou
2010-01-21 2:39 ` anfei zhou
2010-01-21 4:59 ` anfei zhou
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