linux-kernel - Re: [PATCH v2 36/43] powerpc/32: Set current->thread.regs in C interrupt entry

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Date:   Fri, 12 Mar 2021 11:00:10 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 36/43] powerpc/32: Set current->thread.regs in C
 interrupt entry

Excerpts from Christophe Leroy's message of March 11, 2021 10:38 pm:
> 
> 
> Le 11/03/2021 à 11:38, Christophe Leroy a écrit :
>> 
>> 
>> Le 10/03/2021 à 02:33, Nicholas Piggin a écrit :
>>> Excerpts from Christophe Leroy's message of March 9, 2021 10:10 pm:
>>>> No need to do that is assembly, do it in C.
>>>
>>> Hmm. No issues with the patch as such, but why does ppc32 need this but
>>> not 64? AFAIKS 64 sets this when a thread is created.
>> 
>> Looks like ppc64 was doing the same in function save_remaining_regs() in arch/ppc64/kernel/head.S 
>> until commit https://github.com/mpe/linux-fullhistory/commit/e5bb080d
>> 
>> But I can't find what happend to it in that commit.
>> 
>> Where is it done now ? Maybe that's also already done for ppc32.
>> 
> 
> I digged a bit more and found a later bug fix which adds that setting of current->thread.regs at 
> task creation: https://github.com/mpe/linux-fullhistory/commit/3eac1897
> 
> That was in the ppc64 tree only at that time, and was merged into the common powerpc tree via commit 
> https://github.com/mpe/linux-fullhistory/commit/06d67d54

Nice archaeology!

> So we have it for both ppc32 and ppc64 and ppc32 doesn't need to do it at exception entry anymore. 
> I'll remove it.

Good, that's what I hoped (otherwise ppc64 would have been missing 
something).

Thanks,
Nick