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Bug#801259: marked as done (linux-image-4.2.0-1-686-pae: Regression accessing `/dev/mem`)

Your message dated Sun, 09 May 2021 06:44:48 -0700 (PDT)
with message-id <6097e750.1c69fb81.4d31d.f802@mx.google.com>
and subject line Closing this bug (BTS maintenance for src:linux bugs)
has caused the Debian Bug report #801259,
regarding linux-image-4.2.0-1-686-pae: Regression accessing `/dev/mem`
to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.

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-- 
801259: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=801259
Debian Bug Tracking System
Contact owner@bugs.debian.org with problems
--- Begin Message --- 
Package: src:linux
Version: 4.2.3-1
Severity: normal
Tags: upstream

Dear Debian folks,


the coreboot project [1] provides the utility cbmem [2] allowing to
read data from CBMEM (coreboot memory).

If I am not mistaken, it does this by mapping one 1 MB in `/dev/mem`
and then search for a signature.

Since Linux 4.2, this does not work anymore.

	x86/PAT: cbmem:3571 conflicting memory types bfe9c000-bff9c000 uncached-minus<->write-back

Quote [3]:

http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/drivers/firmware/dmi_scan.c?id=d7f96f97c4031fa4ffdb7801f9aae23e96170a6f

That patch added dmi_init() which maintains a persistent dmi mapping.
However, that code used ioremap() as it's mapping. Thus, we have an
uncached-minus PAT entry covering the DMI tables. I'm actually not
sure why they don't just maintain a copy of the tables -- maybe for
eventlog purposes? So that PAT entry will always cause issues w/ cbmem
trying to do brute force 1MiB mappings of /dev/mem.


Thanks,

Paul


[1] http://www.coreboot.org
[2] http://review.coreboot.org/gitweb?p=coreboot.git;a=tree;f=util/cbmem;h=e0a646aa20d57261afea291c2b31620ecfb29609;hb=HEAD
[3] http://coreboot.org/pipermail/coreboot/2015-October/080405.html

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--- End Message ---
--- Begin Message --- 
Hi

This bug was filed for a very old kernel or the bug is old itself
without resolution.

If you can reproduce it with

- the current version in unstable/testing
- the latest kernel from backports

please reopen the bug, see https://www.debian.org/Bugs/server-control
for details.

Regards,
Salvatore

--- End Message ---
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