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Thomas Gleixner f9abe01d5d x86/smp: Make stop_other_cpus() more robust 
commit 1f5e7eb786 upstream.

Tony reported intermittent lockups on poweroff. His analysis identified the
wbinvd() in stop_this_cpu() as the culprit. This was added to ensure that
on SME enabled machines a kexec() does not leave any stale data in the
caches when switching from encrypted to non-encrypted mode or vice versa.

That wbinvd() is conditional on the SME feature bit which is read directly
from CPUID. But that readout does not check whether the CPUID leaf is
available or not. If it's not available the CPU will return the value of
the highest supported leaf instead. Depending on the content the "SME" bit
might be set or not.

That's incorrect but harmless. Making the CPUID readout conditional makes
the observed hangs go away, but it does not fix the underlying problem:

CPU0					CPU1

 stop_other_cpus()
   send_IPIs(REBOOT);			stop_this_cpu()
   while (num_online_cpus() > 1);         set_online(false);
   proceed... -> hang
				          wbinvd()

WBINVD is an expensive operation and if multiple CPUs issue it at the same
time the resulting delays are even larger.

But CPU0 already observed num_online_cpus() going down to 1 and proceeds
which causes the system to hang.

This issue exists independent of WBINVD, but the delays caused by WBINVD
make it more prominent.

Make this more robust by adding a cpumask which is initialized to the
online CPU mask before sending the IPIs and CPUs clear their bit in
stop_this_cpu() after the WBINVD completed. Check for that cpumask to
become empty in stop_other_cpus() instead of watching num_online_cpus().

The cpumask cannot plug all holes either, but it's better than a raw
counter and allows to restrict the NMI fallback IPI to be sent only the
CPUs which have not reported within the timeout window.

Fixes: 08f253ec37 ("x86/cpu: Clear SME feature flag when not in use")
Reported-by: Tony Battersby <tonyb@cybernetics.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Ashok Raj <ashok.raj@intel.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/3817d810-e0f1-8ef8-0bbd-663b919ca49b@cybernetics.com
Link: https://lore.kernel.org/r/87h6r770bv.ffs@tglx
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2023-07-01 13:12:37 +02:00
arch x86/smp: Make stop_other_cpus() more robust 2023-07-01 13:12:37 +02:00
block block: make sure local irq is disabled when calling __blkcg_rstat_flush 2023-06-22 07:44:00 -06:00
certs KEYS: Add missing function documentation 2023-04-24 16:15:52 +03:00
crypto KEYS: asymmetric: Copy sig and digest in public_key_verify_signature() 2023-06-02 15:36:23 +02:00
Documentation Nothing fancy. Two driver and one DT binding fix. 2023-06-25 15:36:01 -07:00
drivers Nothing fancy. Two driver and one DT binding fix. 2023-06-25 15:36:01 -07:00
fs for-6.4-rc7-tag 2023-06-23 16:09:53 -07:00
include - Drop the __weak attribute from a function prototype as it otherwise 2023-06-25 10:13:17 -07:00
init Objtool changes for v6.4: 2023-04-28 14:02:54 -07:00
io_uring io_uring/net: use the correct msghdr union member in io_sendmsg_copy_hdr 2023-06-21 07:34:17 -06:00
ipc Merge branch 'work.namespace' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2023-02-24 19:20:07 -08:00
kernel workqueue: clean up WORK_* constant types, clarify masking 2023-06-23 12:08:14 -07:00
lib 19 hotfixes. 14 are cc:stable and the remainder address issues which were 2023-06-12 16:14:34 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm 19 hotfixes. 8 of these are cc:stable. 2023-06-20 17:20:22 -07:00
net netfilter pull request 23-06-21 2023-06-22 14:39:06 +02:00
rust Rust changes for v6.4 2023-04-30 11:20:22 -07:00
samples samples/bpf: Drop unnecessary fallthrough 2023-05-16 19:44:05 +02:00
scripts - Add a ORC format hash to vmlinux and modules in order for other tools 2023-06-25 10:00:17 -07:00
security selinux: don't use make's grouped targets feature yet 2023-06-01 13:56:13 -04:00
sound ASoC: Fix for v6.4 2023-06-21 15:23:23 +02:00
tools Networking fixes for 6.4-rc8, including fixes from ipsec, bpf, 2023-06-22 17:59:51 -07:00
usr initramfs: Check negative timestamp to prevent broken cpio archive 2023-04-16 17:37:01 +09:00
virt KVM: Avoid illegal stage2 mapping on invalid memory slot 2023-06-22 15:14:57 -04:00
.clang-format cxl for v6.4 2023-04-30 11:51:51 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for *.dtso files 2023-02-26 15:28:23 +09:00
.gitignore linux-kselftest-kunit-6.4-rc1 2023-04-24 12:31:32 -07:00
.mailmap mailmap: add entries for Ben Dooks 2023-06-19 13:19:35 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: sctp: move Neil to CREDITS 2023-05-12 08:51:32 +01:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Networking fixes for 6.4-rc8, including fixes from ipsec, bpf, 2023-06-22 17:59:51 -07:00
Makefile Linux 6.4 2023-06-25 16:29:58 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

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.