From: Linus Torvalds <torvalds@linux-foundation.org>
To: Vitaly Mayatskikh <v.mayatskih@gmail.com>
Cc: linux-kernel@vger.kernel.org, Andi Kleen <andi@firstfloor.org>,
Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH] x86: Optimize tail handling for copy_user
Date: Mon, 28 Jul 2008 08:48:41 -0700 (PDT) [thread overview]
Message-ID: <alpine.LFD.1.10.0807280846320.3486@nehalem.linux-foundation.org> (raw)
In-Reply-To: <m3ljzmdrqh.fsf@gravicappa.englab.brq.redhat.com>
On Mon, 28 Jul 2008, Vitaly Mayatskikh wrote:
>
> Reduce protection faults count in copy_user_handle_tail routine by
> limiting clear length to the end of page as was suggested by Linus.
No, you did it wrong.
The page _clearing_ has to be to the end of the copy. Yes, in practice, I
don't think the kernel actually very often does "copy_from_user()" calls
that are page crossers in the kernel, but they do happen.
It's the _copy_ part that needn't cross pages, because we know that
something faulted, and we _know_ that it wasn't the clearing.
Really: the clearing should be just a "memset()" with no limitations. It
can never fault without it being a serious bug, and then we should not fix
it up, but we should oops!
Linus
next prev parent reply other threads:[~2008-07-28 15:52 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-07-28 14:10 Vitaly Mayatskikh
2008-07-28 15:48 ` Linus Torvalds [this message]
2008-07-29 15:24 ` Vitaly Mayatskikh
2008-07-30 12:02 ` Vitaly Mayatskikh
2008-07-30 17:29 ` Linus Torvalds
2008-07-31 14:27 ` Vitaly Mayatskikh
2008-08-01 20:10 ` Linus Torvalds
2008-08-01 22:04 ` Vitaly Mayatskikh
2008-08-01 22:30 ` Linus Torvalds
2008-08-01 22:53 ` Vitaly Mayatskikh
2008-07-30 12:07 ` Vitaly Mayatskikh
2008-07-30 12:13 ` Vitaly Mayatskikh
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