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Russell Senior 58446f9868 x86/CPU: Fix warm boot hang regression on AMD SC1100 SoC systems
[ Upstream commit bebe35bb738b573c32a5033499cd59f20293f2a3 ]

I still have some Soekris net4826 in a Community Wireless Network I
volunteer with. These devices use an AMD SC1100 SoC. I am running
OpenWrt on them, which uses a patched kernel, that naturally has
evolved over time.  I haven't updated the ones in the field in a
number of years (circa 2017), but have one in a test bed, where I have
intermittently tried out test builds.

A few years ago, I noticed some trouble, particularly when "warm
booting", that is, doing a reboot without removing power, and noticed
the device was hanging after the kernel message:

  [    0.081615] Working around Cyrix MediaGX virtual DMA bugs.

If I removed power and then restarted, it would boot fine, continuing
through the message above, thusly:

  [    0.081615] Working around Cyrix MediaGX virtual DMA bugs.
  [    0.090076] Enable Memory-Write-back mode on Cyrix/NSC processor.
  [    0.100000] Enable Memory access reorder on Cyrix/NSC processor.
  [    0.100070] Last level iTLB entries: 4KB 0, 2MB 0, 4MB 0
  [    0.110058] Last level dTLB entries: 4KB 0, 2MB 0, 4MB 0, 1GB 0
  [    0.120037] CPU: NSC Geode(TM) Integrated Processor by National Semi (family: 0x5, model: 0x9, stepping: 0x1)
  [...]

In order to continue using modern tools, like ssh, to interact with
the software on these old devices, I need modern builds of the OpenWrt
firmware on the devices. I confirmed that the warm boot hang was still
an issue in modern OpenWrt builds (currently using a patched linux
v6.6.65).

Last night, I decided it was time to get to the bottom of the warm
boot hang, and began bisecting. From preserved builds, I narrowed down
the bisection window from late February to late May 2019. During this
period, the OpenWrt builds were using 4.14.x. I was able to build
using period-correct Ubuntu 18.04.6. After a number of bisection
iterations, I identified a kernel bump from 4.14.112 to 4.14.113 as
the commit that introduced the warm boot hang.

  07aaa7e3d6

Looking at the upstream changes in the stable kernel between 4.14.112
and 4.14.113 (tig v4.14.112..v4.14.113), I spotted a likely suspect:

  https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=20afb90f730982882e65b01fb8bdfe83914339c5

So, I tried reverting just that kernel change on top of the breaking
OpenWrt commit, and my warm boot hang went away.

Presumably, the warm boot hang is due to some register not getting
cleared in the same way that a loss of power does. That is
approximately as much as I understand about the problem.

More poking/prodding and coaching from Jonas Gorski, it looks
like this test patch fixes the problem on my board: Tested against
v6.6.67 and v4.14.113.

Fixes: 18fb053f9b ("x86/cpu/cyrix: Use correct macros for Cyrix calls on Geode processors")
Debugged-by: Jonas Gorski <jonas.gorski@gmail.com>
Signed-off-by: Russell Senior <russell@personaltelco.net>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/CAHP3WfOgs3Ms4Z+L9i0-iBOE21sdMk5erAiJurPjnrL9LSsgRA@mail.gmail.com
Cc: Matthew Whitehead <tedheadster@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2025-03-13 12:43:25 +01:00
arch x86/CPU: Fix warm boot hang regression on AMD SC1100 SoC systems 2025-03-13 12:43:25 +01:00
block partitions: mac: fix handling of bogus partition table 2025-03-13 12:43:16 +01:00
certs
crypto crypto: testmgr - some more fixes to RSA test vectors 2025-03-13 12:43:21 +01:00
Documentation dt-bindings: mmc: controller: clarify the address-cells description 2025-03-13 12:42:53 +01:00
drivers net: mvpp2: cls: Fixed Non IP flow, with vlan tag flow defination. 2025-03-13 12:43:24 +01:00
fs btrfs: avoid monopolizing a core when activating a swap file 2025-03-13 12:43:19 +01:00
include net: extract port range fields from fl_flow_key 2025-03-13 12:43:23 +01:00
init initramfs: avoid filename buffer overrun 2024-12-14 19:44:21 +01:00
ipc
kernel acct: block access to kernel internal filesystems 2025-03-13 12:43:23 +01:00
lib lib: string_helpers: silence snprintf() output truncation warning 2024-12-14 19:44:39 +01:00
LICENSES
mm memcg: fix soft lockup in the OOM process 2025-03-13 12:43:21 +01:00
net ipvs: Always clear ipvs_property flag in skb_scrub_packet() 2025-03-13 12:43:24 +01:00
samples samples/bpf: Fix a resource leak 2024-12-14 19:44:50 +01:00
scripts kbuild: Move -Wenum-enum-conversion to W=2 2025-03-13 12:43:09 +01:00
security ima: Fix use-after-free on a dentry's dname.name 2025-03-13 12:43:19 +01:00
sound ASoC: es8328: fix route from DAC to output 2025-03-13 12:43:24 +01:00
tools perf bench: Fix undefined behavior in cmpworker() 2025-03-13 12:43:08 +01:00
usr
virt KVM: arm64: Ignore PMCNTENSET_EL0 while checking for overflow status 2024-12-19 18:05:04 +01:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore Remove *.orig pattern from .gitignore 2024-11-08 16:20:33 +01:00
.mailmap
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS
Makefile kbuild: userprogs: use correct lld when linking through clang 2025-03-13 12:43:04 +01:00
README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.