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Subject: Re: [PATCH RESEND v3 6/6] powerpc/signal: Use
 unsafe_copy_siginfo_to_user()
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>, hch@infradead.org,
        linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
References: <1718f38859d5366f82d5bef531f255cedf537b5d.1631537060.git.christophe.leroy@csgroup.eu>
 <2b179deba4fd4ec0868cdc48a0230dfa3aa5a22f.1631537060.git.christophe.leroy@csgroup.eu>
 <87h7eopixa.fsf@disp2133> <87y280o38q.fsf@disp2133>
From:   Christophe Leroy <christophe.leroy@csgroup.eu>
Message-ID: <96d06ad9-5a9b-b8c3-3c1d-ed8837091a60@csgroup.eu>
Date:   Mon, 13 Sep 2021 19:19:26 +0200
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Le 13/09/2021 à 18:21, Eric W. Biederman a écrit :
> ebiederm@xmission.com (Eric W. Biederman) writes:
> 
>> Christophe Leroy <christophe.leroy@csgroup.eu> writes:
>>
>>> Use unsafe_copy_siginfo_to_user() in order to do the copy
>>> within the user access block.
>>>
>>> On an mpc 8321 (book3s/32) the improvment is about 5% on a process
>>> sending a signal to itself.
> 
> If you can't make function calls from an unsafe macro there is another
> way to handle this that doesn't require everything to be inline.
> 
>  From a safety perspective it is probably even a better approach.

Yes but that's exactly what I wanted to avoid for the native ppc32 case: 
this double hop means useless pressure on the cache. The siginfo_t 
structure is 128 bytes large, that means 8 lines of cache on powerpc 8xx.

But maybe it is acceptable to do that only for the compat case. Let me 
think about it, it might be quite easy.

Christophe