From: Andrew Morton <akpm@osdl.org>
To: David Miller <davem@davemloft.net>
Cc: dmonakhov@openvz.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] mm:D-cache aliasing issue in cow_user_page
Date: Thu, 19 Oct 2006 00:17:47 -0700 [thread overview]
Message-ID: <20061019001747.7da58920.akpm@osdl.org> (raw)
In-Reply-To: <20061019.000027.41635681.davem@davemloft.net>
On Thu, 19 Oct 2006 00:00:27 -0700 (PDT)
David Miller <davem@davemloft.net> wrote:
> > > 1452 if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE))
> > > 1453 memset(kaddr, 0, PAGE_SIZE);
> > > 1454 kunmap_atomic(kaddr, KM_USER0);
> > > #### D-cache have to be flushed here.
> > > #### It seems it is just forgotten.
> > >
> > > 1455 return;
> > > 1456
> > > 1457 }
> > > 1458 copy_user_highpage(dst, src, va);
> > > #### Ok here. flush_dcache_page() called from this func if arch need it
> > > 1459 }
> > >
> >
> > This page has just been allocated and is private to the caller - there can
> > be no userspace mappings of it.
>
> Unfortunately, the kernel has just touched the page and thus there are
> active cache lines for the kernel side mapping. When we map this into
> user space, userspace might see stale cachelines instead of the
> memset() stores.
hm. Has it always been that way or did something change?
> Architectures typically take care of this in copy_user_page() and
> clear_user_page(). The absolutely depend upon those two routines
> being used for anonymous pages, and handle the D-cache issues there.
Only anonymous pages? There are zillions of places where we modify
pagecache without a flush, especially against the blockdev mapping (fs
metadata).
> But this code is going outside of that scope, and therefore needs
> an explicit D-cache flush.
OK, I'll add the patch.
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next prev parent reply other threads:[~2006-10-19 7:17 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-10-17 9:15 Dmitriy Monakhov
2006-10-19 6:33 ` Andrew Morton
2006-10-19 7:00 ` David Miller, Andrew Morton
2006-10-19 7:17 ` Andrew Morton [this message]
2006-10-19 7:22 ` David Miller, Andrew Morton
2006-10-19 7:41 ` Andrew Morton
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