linux-kernel - Re: [PATCH 1/3] x86: drop unnecessary kernel

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Message-ID: <20110705132825.GA3900@sun>
Date:	Tue, 5 Jul 2011 17:28:25 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Ian Campbell <ian.campbell@...rix.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Brian Gerst <brgerst@...il.com>,
	Jan Beulich <JBeulich@...ell.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>, x86@...nel.org
Subject: Re: [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64
 bit.

On Tue, Jul 05, 2011 at 02:00:12PM +0100, Ian Campbell wrote:
> For no reason that I can determine 64 bit x86 saves the current eflags
> in cpu_init purely for use in ret_from_fork. The equivalent 32 bit
> code simply hard codes 0x0202 as the new EFLAGS which seems safer than
> relying on a potentially arbitrary EFLAGS saved during cpu_init.
> 
> Original i386 changeset
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=47a5c6fa0e204a2b63309c648bb2fde36836c826
> Original x86_64 changset
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=658fdbef66e5e9be79b457edc2cbbb3add840aa9
> 
> The only comment in the later indicates that it is following the
> former, but not why it differs in this way.
> 
> This change makes 64 bit use the same mechanism to setup the initial
> EFLAGS on fork. Note that 64 bit resets EFLAGS before calling
> schedule_tail() as opposed to 32 bit which calls schedule_tail()
> first. Therefore the correct value for EFLAGS has opposite IF
> bit. This will be fixed in a subsequent patch.
> 
> Signed-off-by: Ian Campbell <ian.campbell@...rix.com>
> Cc: x86@...nel.org

The whole series looks good to me, thanks Ian! I hope I don't
miss anything, so lets wait for more feedback ;)

	Cyrill
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