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

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Date:	Thu, 21 May 2015 10:12:04 +0100
From:	Paul Burton <paul.burton@...tec.com>
To:	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>
CC:	<linux-mips@...ux-mips.org>, <rusty@...tcorp.com.au>,
	<alexinbeijing@...il.com>, <david.daney@...ium.com>,
	<alex@...x-smith.me.uk>, <linux-kernel@...r.kernel.org>,
	<ralf@...ux-mips.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 Tue, May 19, 2015 at 02:13:51PM -0700, Leonid Yegoshin wrote:
> During thread cloning the new (child) thread should have MSA disabled even
> at first thread entry. So, the code to disable MSA is moved from macro
> 'switch_to' to assembler function 'resume' before it switches kernel stack
> to 'next' (new) thread. Call of 'disable_msa' after 'resume' in 'switch_to'
> macro never called a first time entry into thread.

Hi Leonid,

I'm not sure I understand what you're trying to say here. Do you have an
example of a program that demonstrates the behaviour you believe to be
broken?

Thanks,
    Paul

> Signed-off-by: Leonid Yegoshin <Leonid.Yegoshin@...tec.com>
> ---
>  arch/mips/include/asm/switch_to.h |    1 -
>  arch/mips/kernel/r4k_switch.S     |    6 ++++++
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/mips/include/asm/switch_to.h b/arch/mips/include/asm/switch_to.h
> index e92d6c4b5ed1..0d0f7f8f8b3a 100644
> --- a/arch/mips/include/asm/switch_to.h
> +++ b/arch/mips/include/asm/switch_to.h
> @@ -104,7 +104,6 @@ do {									\
>  	if (test_and_clear_tsk_thread_flag(prev, TIF_USEDMSA))		\
>  		__fpsave = FP_SAVE_VECTOR;				\
>  	(last) = resume(prev, next, task_thread_info(next), __fpsave);	\
> -	disable_msa();							\
>  } while (0)
>  
>  #define finish_arch_switch(prev)					\
> diff --git a/arch/mips/kernel/r4k_switch.S b/arch/mips/kernel/r4k_switch.S
> index 04cbbde3521b..7dbb64656bfe 100644
> --- a/arch/mips/kernel/r4k_switch.S
> +++ b/arch/mips/kernel/r4k_switch.S
> @@ -25,6 +25,7 @@
>  /* preprocessor replaces the fp in ".set fp=64" with $30 otherwise */
>  #undef fp
>  
> +#define t4  $12
>  /*
>   * Offset to the current process status flags, the first 32 bytes of the
>   * stack are not used.
> @@ -73,6 +74,11 @@
>  	cfc1	t1, fcr31
>  	msa_save_all	a0
>  	.set pop	/* SET_HARDFLOAT */
> +	li      t4, MIPS_CONF5_MSAEN
> +	mfc0    t3, CP0_CONFIG, 5
> +	or      t3, t3, t4
> +	xor     t3, t3, t4
> +	mtc0    t3, CP0_CONFIG, 5
>  
>  	sw	t1, THREAD_FCR31(a0)
>  	b	2f
> 

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