linux-kernel - /dev/mem arch/x86 mm/pat.c break

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Message-ID: <Pine.LNX.4.21.1610240540340.31299-100000@shell.dhp.com>
Date:   Mon, 24 Oct 2016 05:58:58 +0000 (/etc/localtime)
From:   n@....com
To:     linux-kernel@...r.kernel.org
Subject: /dev/mem arch/x86 mm/pat.c break

Hi,

Unless I read C wrong, pat.c seems to break all non-strict devmem use.  I
discovered this while reversing a bunch of pci and other low-level
stuff.  Here is a link to the fix, http//users.dhp.com/~n/pubs/
the one starting with Linux-86...txt is the correct file, those kernel
bugs in OpenBSD and that are just hilarious enough to keep around.. 

Oh, here is the full link:
http://users.dhp.com/~n/Linux-x86-mmap-nonstrict-broken.txt

This was first 'nonpromisc_devmem', probably dating back to that
introduction of 1MB limits on mmap(2) way back in the day.. who knows.

Alright, I confess as a kernel programmer Linux isn't my thing, I prefer
Unix particularly BSD and SysV (SVR4 would be sort of both).  Thats mostly
because sys_call_table is sysent to me, as are tons of other symbols.  But
still, /usr/libexec/cpp seems to have broken /dev/mem
mmap(2) functionality over the non-strict range of memory for.. a long
time.

If I'm wrong, then there is no problem, however I had to fix this to get
things working.  Thanks, I realize that #ifdef instead of #ifndef can
cause strictness reversals.. good thing other portions of the kernel had
this correct, or strict would be nonstrict, and vice-versa.  Alright,
enjoy..

Reply address: n@....net (please).

-n