linux-kernel - Re: [PATCH v7 2/2] ARM: ftrace: Add MODULE

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Message-ID: <ad517652-edc7-7f0d-f768-2cd7ed1298e6@nokia.com>
Date:   Mon, 15 Mar 2021 10:19:37 +0100
From:   Alexander Sverdlin <alexander.sverdlin@...ia.com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        Qais Yousef <qais.yousef@....com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [PATCH v7 2/2] ARM: ftrace: Add MODULE_PLTS support

Hello Florian,

On 12/03/2021 19:35, Florian Fainelli wrote:
>>> https://www.spinics.net/lists/arm-kernel/msg878599.html
>> I am testing with your module. I can't reproduce the problem you describe with
>> it as I stated.
>>
>> I will try to spend more time on it on the weekend.
> Alexander, do you load one or multiple instances of that fat module?

One cannot have "multiple instances of the same module"...

> The test module does a 6 * 1024 * 1024 / 2 = 3 million repetitions of
> the "nop" instruction which should be 32-bits wide in ARM mode and
> 16-bits wide in Thumb mode, right?
> 
> In ARM mode we have a 14MB module space, so 3 * 1024 * 1024 * 4 = 12MB,
> which should still fit within if you have no module loaded, however a
> second instance of the module should make us spill into vmalloc space.
> 
> In Thumb mode, we have a 6MB module space, so 3 * 1024 * 1024 * 2 = 6MB
> so we may spill, but maybe not.
> 
> I was not able to reproduce the warning with just one module, but with
> two (cannot have the same name BTW), it kicked in.

... well, may be the size was arbitrary chosen to not fit into our module space
and we have more modules already loaded. But you are free to adjust the 
amount of NOPs! :)

-- 
Best regards,
Alexander Sverdlin.