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

From: "H. Peter Anvin" <[email-masked]>
Date: Mon, 11 Aug 2008 12:24:59 -0700

Ingo Molnar wrote:
> * Suresh Siddha <[email-masked]> wrote:
> 
>> Reported-and-bisected-by: Wolfgang Walter <[email-masked]>
>> Signed-off-by: Suresh Siddha <[email-masked]>
> 
> 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