Re: [PATCH] powerpc: Clear user CPU feature bits if TM is disabled at runtime

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Apr 04, 2016 at 09:11:12PM +1000, Anton Blanchard wrote:
> In check_cpu_pa_features() we check a number of bits in the
> ibm,pa-features array and set and clear CPU features based on what
> we find. One of these bits is CPU_FTR_TM, the transactional memory
> feature bit.
> 
> If this does disable TM at runtime, then we need to tell userspace
> about it by clearing the user CPU feature bits.
> 
> Without this patch userspace processes will think they can execute
> TM instructions and get killed when they try.
> 
> Signed-off-by: Anton Blanchard <anton@samba.org>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> Cc: stable@vger.kernel.org
> ---
> 
> Michael I've added stable here because I'm seeing this on a number
> of distros and would like to get it backported, but I'll leave it up
> to you if it should go there.
> 
> diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
> index f98be83..98c6c86 100644
> --- a/arch/powerpc/kernel/setup_64.c
> +++ b/arch/powerpc/kernel/setup_64.c
> @@ -822,4 +822,18 @@ static int __init disable_hardlockup_detector(void)
>  	return 0;
>  }
>  early_initcall(disable_hardlockup_detector);
> +
> +static int __init update_cpu_user_features(void)
> +{
> +	/*
> +	 * Firmware might have disabled TM by clearing the relevant
> +	 * bit in the ibm,pa-features array. In this case we need to
> +	 * tell userspace.
> +	 */
> +	if (!cpu_has_feature(CPU_FTR_TM))
> +		cur_cpu_spec->cpu_user_features2 &= ~(PPC_FEATURE2_HTM|PPC_FEATURE2_HTM_NOSC);
> +
> +	return 0;
> +}
> +early_initcall(update_cpu_user_features);
>  #endif
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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