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Message-ID: <alpine.LFD.1.10.0808011524150.6819@nehalem.linux-foundation.org>
Date: Fri, 1 Aug 2008 15:30:26 -0700 (PDT)
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Vitaly Mayatskikh <v.mayatskih@...il.com>
cc: linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>,
Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] x86: Optimize tail handling for copy_user
On Sat, 2 Aug 2008, Vitaly Mayatskikh wrote:
>
> Well, I have sanity test for it (at http://people.redhat.com/vmayatsk/copy_user_x8664/),
> but unfortunately it shows what I want to see, not the truth. I'm going
> to make a large regression testing next week.
I was actually thinking more along the lines of actually doing a
test-suite with the few most relevant system calls (to catch the few cases
that matter), and judicious use of mmap/munmap to make sure to trigger it
in-kernel.
It probably doesn't really need all that many system calls to trigger all
the relevant paths. A "read()" should trigger the "to_user()" case, and a
write() to a file should trigger the 'from_user_nocache()" case. And while
the "from_user()" case with zeroing migth be harder to see (because all
_normal_ users should also look at the error case and return EFAULT), I
think there are a few cases where we just depend on the zeroing.
Doing a
git grep ' copy_from_user('
(that's a tab in that grep thing) shows at least the termios code doing
it, for example. But fewer cases than I expected.
Linus
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