linux-kernel - Re: [PATCH 1/2] MIPS: MSA: bugfix - disable MSA during thread switch correctly

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Date:	Fri, 22 May 2015 17:00:42 -0700
From:	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>
To:	Ralf Baechle <ralf@...ux-mips.org>
CC:	<linux-mips@...ux-mips.org>, <rusty@...tcorp.com.au>,
	<alexinbeijing@...il.com>, <paul.burton@...tec.com>,
	<david.daney@...ium.com>, <alex@...x-smith.me.uk>,
	<linux-kernel@...r.kernel.org>, <james.hogan@...tec.com>,
	<markos.chandras@...tec.com>, <macro@...ux-mips.org>,
	<eunb.song@...sung.com>, <manuel.lauss@...il.com>,
	<andreas.herrmann@...iumnetworks.com>
Subject: Re: [PATCH 1/2] MIPS: MSA: bugfix - disable MSA during thread switch
 correctly

On 05/22/2015 04:20 PM, Ralf Baechle wrote:
> On Fri, May 22, 2015 at 11:37:34AM -0700, Leonid Yegoshin wrote:
>
>> On 05/22/2015 02:38 AM, Ralf Baechle wrote:
>>> Just move the call to finish_arch_switch().
>> It might be a problem later, then a correct MSA partiton starts working. It
>> should be tight to saving MSA registers in that case.
>>
>>> Your rewrite also dropped the if (cpu_has_msa) condition from
>>> disable_msa() probably causing havoc on lots of CPUs which will likely not
>>> decode the set bits of the MFC0/MTC0 instructions thus end up accessing
>>> Config0. Ralf
>> Right before this chunk of code there is a saving MSA registers. Does it
>> causing a havoc or else?
>>
>> May I ask you to look into switch_to macro to figure out how "if
>> (cpu_has_msa)" check works in this case?
> Ah sorry I now see that your added code is not executed for all CPUs but
> only those having MSA.  So then it's safe.
>
> Still I don't stylistically like defining the register t4 in the middle
> of the code.
>
> Below my suggested patch.  It's advantage is that for non-MSA platforms
> the call to disable_msa() will be removed entirely.
>
> Something like Paul's http://patchwork.linux-mips.org/patch/10111/ (assuming
> it's correct and tested) seems like a full cleanup but it's way too
> complex for 4.1 or the stable kernels.
>
>    Ralf
>
>
All 3 patches seems working (I tested), but if you don't like mine then 
I prefer Paul's patch more - it concentrates stuff more closely and 
removes some assembly stuff.

Besides that, it introduces lose_fpu_inatomic() which is needed for me :)

- Leonid.

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