linux-kernel - Re: [PATCH v2 1/3] s390/cpufeature: rework to allow more than only hwcap bits

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Date:   Fri, 15 Jul 2022 11:32:06 +0200
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Hendrik Brueckner <brueckner@...ux.ibm.com>
Cc:     Steffen Eiden <seiden@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, nrb@...ux.ibm.com
Subject: Re: [PATCH v2 1/3] s390/cpufeature: rework to allow more than only
 hwcap bits

On Fri, Jul 15, 2022 at 09:59:49AM +0200, Hendrik Brueckner wrote:
> Regarding facility bits for cpu features:  Initially, I used
> MSA hwcap to cover all ciphers among all hw generations. With facility bit
> checks, it makes more sense to fine-tune and load based on respective
> MSA level or CPACF functions that is required for ciphers/hashes.
...
> > -module_cpu_feature_match(MSA, init);
> > +module_cpu_feature_match(S390_CPU_FEATURE_MSA, init);
> >  module_exit(fini);
> 
> which becomes automatically loaded if (any) MSA is available and then
> performs this check:
> 
> 	cpacf_query_func(CPACF_KIMD, CPACF_KIMD_SHA_512
> 
> which in the worst case would fail.
> 
> This might be a very useful follow-up patch to remove those mod init checks
> into the cpu feature.

Yes, that makes a lot of sense. Thanks for suggesting this!