linux-kernel - Re: [PATCH v4 10/24] crypto: x86/poly

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Message-ID: <Y47El6TRitHm7Xz9@gondor.apana.org.au>
Date:   Tue, 6 Dec 2022 12:27:03 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     "Elliott, Robert (Servers)" <elliott@....com>
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "tim.c.chen@...ux.intel.com" <tim.c.chen@...ux.intel.com>,
        "ap420073@...il.com" <ap420073@...il.com>,
        "ardb@...nel.org" <ardb@...nel.org>,
        "David.Laight@...lab.com" <David.Laight@...lab.com>,
        "ebiggers@...nel.org" <ebiggers@...nel.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 10/24] crypto: x86/poly - limit FPU preemption

On Fri, Dec 02, 2022 at 04:15:23PM +0000, Elliott, Robert (Servers) wrote:
> 
> 
> > -----Original Message-----
> > From: Herbert Xu <herbert@...dor.apana.org.au>
> > Sent: Friday, December 2, 2022 3:25 AM
> > To: Elliott, Robert (Servers) <elliott@....com>
> > Subject: Re: [PATCH v4 10/24] crypto: x86/poly - limit FPU preemption
> > 
> > On Fri, Dec 02, 2022 at 06:21:02AM +0000, Elliott, Robert (Servers) wrote:
> ...
> > BTW, just a minor nit but you can delete the cond_resched() call
> > because kernel_fpu_end()/preempt_enable() will do it anyway.
> 
> That happens under
> 	CONFIG_PREEMPTION=y
> (from include/Linux/preempt.h and arch/x86/include/asm/preempt.h)
> 
> Is calling cond_resched() still helpful if that is not the configuration?

Perhaps, but then again perhaps if preemption is off, maybe we
shouldn't even bother with the 4K split.  Were the initial
warnings with or without preemption?

Personally I don't really care since I always use preemption.

The PREEMPT Kconfigs do provide a bit of nuance with the split
between PREEMPT_NONE vs. PREEMPT_VOLUNTARY.  But perhaps that is
just overkill for our situation.

I'll leave it to you to decide :)

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