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From: Eric Biggers <ebiggers@kernel.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-crypto@vger.kernel.org,
	Herbert Xu <herbert@gondor.apana.org.au>,
	"David S. Miller" <davem@davemloft.net>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] crypto: testmgr - Only disable migration in crypto_disable_simd_for_test()
Date: Tue, 5 Oct 2021 11:17:16 -0700	[thread overview]
Message-ID: <YVyWrKUk81e10zM7@gmail.com> (raw)
In-Reply-To: <20210928115401.441339-1-bigeasy@linutronix.de>

Hi Sebastian,

On Tue, Sep 28, 2021 at 01:54:01PM +0200, Sebastian Andrzej Siewior wrote:
> crypto_disable_simd_for_test() disables preemption in order to receive a
> stable per-CPU variable which it needs to modify in order to alter
> crypto_simd_usable() results.
> 
> This can also be achived by migrate_disable() which forbidds CPU
> migrations but allows the task to be preempted. The latter is important
> for PREEMPT_RT since operation like skcipher_walk_first() may allocate
> memory which must not happen with disabled preemption on PREEMPT_RT.
> 
> Use migrate_disable() in crypto_disable_simd_for_test() to achieve a
> stable per-CPU pointer.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

The comment above the definition of migrate_disable() in include/linux/preempt.h
claims that it is a temporary workaround.

Is there a better way to do this that should be used instead?

- Eric

  reply	other threads:[~2021-10-05 18:17 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-28 11:54 [PATCH] crypto: testmgr - Only disable migration in crypto_disable_simd_for_test() Sebastian Andrzej Siewior
2021-10-05 18:17 ` Eric Biggers [this message]
2021-10-07  9:42   ` Sebastian Andrzej Siewior
2021-10-07 17:53     ` Eric Biggers
2021-10-07 19:03       ` Sebastian Andrzej Siewior
2021-10-08 11:34         ` Herbert Xu
2021-10-08 12:24 ` Herbert Xu

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