linux-kernel - Re: [PATCH] powerpc/8xx: Load modules closer to kernel text

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Message-ID: <7ff6c893-8dcb-3908-3b6c-7172bc224c77@csgroup.eu>
Date:   Thu, 1 Apr 2021 15:43:52 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Jordan Niethe <jniethe5@...il.com>
Subject: Re: [PATCH] powerpc/8xx: Load modules closer to kernel text



Le 01/04/2021 à 06:33, Michael Ellerman a écrit :
> Christophe Leroy <christophe.leroy@...roup.eu> writes:
>> Le 31/03/2021 à 15:39, Michael Ellerman a écrit :
>>> Christophe Leroy <christophe.leroy@...roup.eu> writes:
>>>> On the 8xx, TASK_SIZE is 0x80000000. The space between TASK_SIZE and
>>>> PAGE_OFFSET is not used.
>>>>
>>>> Use it to load modules in order to minimise the distance between
>>>> kernel text and modules and avoid trampolines in modules to access
>>>> kernel functions or other module functions.
>>>>
>>>> Define a 16Mbytes area for modules, that's more than enough.
>>>
>>> 16MB seems kind of small.
>>>
>>> At least on 64-bit we could potentially have hundreds of MBs of modules.
>>>
>>
>> Well, with a 16 MB kernel and 16 MB modules, my board is full :)
> 
> Heh.

ARM set it to 16M or 8M.

> 
>> Even on the more recent board that has 128 MB, I don't expect more than a few MBs of modules in
>> addition to the kernel which is approx 8M.
>>
>> But ok, I'll do something more generic, though it will conflict with Jordan's series.
> 
> Don't feel you have to. You're the expert on 8xx, not me.
> 

Doing it generic allows to also get it on book3s/32 for free.

Christophe