linux-kernel - Re: [PATCH] TIF_NOTSC and SECCOMP prctl

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Date:	Tue, 18 Jul 2006 06:20:20 -0400
From:	Chuck Ebbert <76306.1226@...puserve.com>
To:	"andrea@...share.com" <andrea@...share.com>
Cc:	"bruce@...rew.cmu.edu" <bruce@...rew.cmu.edu>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Arjan van de Ven <arjan@...radead.org>,
	Adrian Bunk <bunk@...sta.de>,
	Lee Revell <rlrevell@...-job.com>,
	Linus Torvalds <torvalds@...l.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] TIF_NOTSC and SECCOMP prctl

In-Reply-To: <20060714060932.GE18774@...eron.random>

On Fri, 14 Jul 2006 08:09:32 +0200, andrea@...share.com wrote:

> The below patch seems to work, I ported all my client code on top of
> prctl already. (it's a bit more painful to autodetect a kernel with
> CONFIG_SECCOMP turned off but I already adapted to it)

AFAIC the /proc method of controlling seccomp is so ugly it should
just go, but what about backwards compatibility?

I have a couple of questions:


+void disable_TSC(void)
+{
+       if (!test_and_set_thread_flag(TIF_NOTSC))
+               /*
+                * Must flip the CPU state synchronously with
+                * TIF_NOTSC in the current running context.
+                */
+               hard_disable_TSC();
+}

This gets called from sys_prctl().  Do you need to worry about preemption
between the test_and_set and TSC disable?


--- a/include/asm-i386/processor.h      Thu Jul 13 03:03:35 2006 +0700
+++ b/include/asm-i386/processor.h      Fri Jul 14 07:47:57 2006 +0200
@@ -256,6 +256,10 @@ static inline void clear_in_cr4 (unsigne
        cr4 &= ~mask;
        write_cr4(cr4);
 }
+
+extern void hard_disable_TSC(void);
+extern void disable_TSC(void);
+extern void hard_enable_TSC(void);

Maybe these should be inline?  They're really small and that way you
don't need #ifdef around the code for them.


> Reviews are welcome (then I will move into x86-64, all other archs
> supporting seccomp should require no changes despite the API
> change). Thanks.

For x86_64 you need this:

ftp://ftp.firstfloor.org/pub/ak/x86_64/quilt-current/patches/tif-flags-for-debug-regs-and-io-bitmap-in-ctxsw

But I don't think Andi plans on pushing it for 2.6.18.

-- 
Chuck
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