linux-kernel - Re: simd: Allow simd use in kernel threads with softirqs disabled

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Date:	Fri, 14 Nov 2014 17:17:05 +0100
From:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Suresh Siddha <sbsiddha@...il.com>,
	Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Steffen Klassert <steffen.klassert@...unet.com>,
	Ming Liu <ming.liu@...driver.com>
Subject: Re: simd: Allow simd use in kernel threads with softirqs disabled

On 14 November 2014 16:43, Herbert Xu <herbert@...dor.apana.org.au> wrote:
> While working on the cryptd request reordering problem, I noticed
> an anomaly where kernel threads are normally allowed to use simd
> per may_use_simd, but as soon as you disable softirqs, they suddenly
> lose that ability for no good reason.
>
> The problem is that in_interrupt does not distinguish between
> softirq processing and simply having softirqs disabled.  This
> patch creates a new helper in_serving_interrupt which makes that
> distinction.  It then uses this in all current implementations
> of may_use_simd.
>

Isn't that a much more widespread problem if in_interrupt() yields
true while no interrupt is being served?

> Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
>
> diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
> index a9a4229..6cdaa852 100644
> --- a/arch/x86/kernel/i387.c
> +++ b/arch/x86/kernel/i387.c
> @@ -63,7 +63,7 @@ static inline bool interrupted_user_mode(void)
>   */
>  bool irq_fpu_usable(void)
>  {
> -       return !in_interrupt() ||
> +       return !in_serving_interrupt() ||
>                 interrupted_user_mode() ||
>                 interrupted_kernel_fpu_idle();
>  }
> diff --git a/include/asm-generic/simd.h b/include/asm-generic/simd.h
> index f57eb7b..74e0b05 100644
> --- a/include/asm-generic/simd.h
> +++ b/include/asm-generic/simd.h
> @@ -10,5 +10,5 @@
>   */
>  static __must_check inline bool may_use_simd(void)
>  {
> -       return !in_interrupt();
> +       return !in_serving_interrupt();
>  }
> diff --git a/include/linux/preempt_mask.h b/include/linux/preempt_mask.h
> index dbeec4d..18f3b46 100644
> --- a/include/linux/preempt_mask.h
> +++ b/include/linux/preempt_mask.h
> @@ -65,6 +65,8 @@
>  #define in_softirq()           (softirq_count())
>  #define in_interrupt()         (irq_count())
>  #define in_serving_softirq()   (softirq_count() & SOFTIRQ_OFFSET)
> +#define in_serving_interrupt() (irq_count() & (HARDIRQ_MASK | \
> +                                               SOFTIRQ_OFFSET | NMI_MASK))
>
>  /*
>   * Are we in NMI context?
>
> Thanks,
> --
> Email: Herbert Xu <herbert@...dor.apana.org.au>
> Home Page: http://gondor.apana.org.au/~herbert/
> PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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