linux-kernel - Re: [PATCH] x86: only use ERMS for user copies for larger sizes

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Message-ID: <20181123164052.cjbm5ekqigvfpl7t@treble>
Date:   Fri, 23 Nov 2018 10:40:52 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>, pabeni@...hat.com,
        Jens Axboe <axboe@...nel.dk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, bp@...en8.de,
        Peter Anvin <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>, dvlasenk@...hat.com,
        brgerst@...il.com,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: only use ERMS for user copies for larger sizes

On Thu, Nov 22, 2018 at 12:13:41PM +0100, Ingo Molnar wrote:
> Note to self: watch out for patches that change altinstructions and don't 
> make premature vmlinux size impact assumptions. :-)

I noticed a similar problem with ORC data.  As it turns out, size's
"text" calculation also includes read-only sections.  That includes
.rodata and anything else not writable.

Maybe we need a more sensible "size" script for the kernel.  It would be
trivial to implement based on the output of "readelf -S vmlinux".

-- 
Josh