netdev - Re: Kernel oops with 2.6.26, padlock and ipsec: probably problem with fpu state changes

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Message-ID: <48A0920B.30306@zytor.com>
Date:	Mon, 11 Aug 2008 12:24:59 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Suresh Siddha <suresh.b.siddha@...el.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Wolfgang Walter <wolfgang.walter@...m.de>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"viro@...IV.linux.org.uk" <viro@...iv.linux.org.uk>,
	"vegard.nossum@...il.com" <vegard.nossum@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Kernel oops with 2.6.26, padlock and ipsec: probably problem
 with fpu state changes

Ingo Molnar wrote:
> * Suresh Siddha <suresh.b.siddha@...el.com> wrote:
> 
>> Reported-and-bisected-by: Wolfgang Walter <wolfgang.walter@...m.de>
>> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
> 
> no fundamental objection to the x86 bits.
> 
> shouldnt this:
> 
> +       if (!in_interrupt())
> +               return 0;
> 
> just be eliminated and the cr0/TS save/restore be made unconditional?  
> irq-assymetric APIs are not nice in general.
> 
> Reading/setting cr0 isnt _that_ slow. (or if it is, by how much does it 
> slow things down, exactly?)
> 

Setting it is relatively slow.  I think that's part of the reason for 
special instructions to muck with the TS flag.

Reading it might be slow on obsolete processors.

	-hpa
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