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Will Deacon cfb00a3578 arm64: jump_label: Ensure patched jump_labels are visible to all CPUs 
Although the Arm architecture permits concurrent modification and
execution of NOP and branch instructions, it still requires some
synchronisation to ensure that other CPUs consistently execute the newly
written instruction:

 >  When the modified instructions are observable, each PE that is
 >  executing the modified instructions must execute an ISB or perform a
 >  context synchronizing event to ensure execution of the modified
 >  instructions

Prior to commit f6cc0c5016 ("arm64: Avoid calling stop_machine() when
patching jump labels"), the arm64 jump_label patching machinery
performed synchronisation using stop_machine() after each modification,
however this was problematic when flipping static keys from atomic
contexts (namely, the arm_arch_timer CPU hotplug startup notifier) and
so we switched to the _nosync() patching routines to avoid "scheduling
while atomic" BUG()s during boot.

In hindsight, the analysis of the issue in f6cc0c5016 isn't quite
right: it cites the use of IPIs in the default patching routines as the
cause of the lockup, whereas stop_machine() does not rely on IPIs and
the I-cache invalidation is performed using __flush_icache_range(),
which elides the call to kick_all_cpus_sync(). In fact, the blocking
wait for other CPUs is what triggers the BUG() and the problem remains
even after f6cc0c5016, for example because we could block on the
jump_label_mutex. Eventually, the arm_arch_timer driver was fixed to
avoid the static key entirely in commit a862fc2254
("clocksource/arm_arch_timer: Remove use of workaround static key").

This all leaves the jump_label patching code in a funny situation on
arm64 as we do not synchronise with other CPUs to reduce the likelihood
of a bug which no longer exists. Consequently, toggling a static key on
one CPU cannot be assumed to take effect on other CPUs, leading to
potential issues, for example with missing preempt notifiers.

Rather than revert f6cc0c5016 and go back to stop_machine() for each
patch site, implement arch_jump_label_transform_apply() and kick all
the other CPUs with an IPI at the end of patching.

Cc: Alexander Potapenko <glider@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Fixes: f6cc0c5016 ("arm64: Avoid calling stop_machine() when patching jump labels")
Signed-off-by: Will Deacon <will@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240731133601.3073-1-will@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2024-08-02 15:07:01 +01:00
arch arm64: jump_label: Ensure patched jump_labels are visible to all CPUs 2024-08-02 15:07:01 +01:00
block block: fix deadlock between sd_remove & sd_release 2024-07-24 09:51:21 -06:00
certs kbuild: use $(src) instead of $(srctree)/$(src) for source directory 2024-05-10 04:34:52 +09:00
crypto crypto: testmgr - generate power-of-2 lengths more often 2024-07-13 11:50:28 +12:00
Documentation arm64: errata: Expand speculative SSBS workaround (again) 2024-08-01 16:11:28 +01:00
drivers minmax: add a few more MIN_T/MAX_T users 2024-07-28 13:41:14 -07:00
fs This pull request contains updates (actually, just fixes) for UBI and UBIFS: 2024-07-28 11:51:51 -07:00
include minmax: simplify and clarify min_t()/max_t() implementation 2024-07-28 13:50:01 -07:00
init rust: SHADOW_CALL_STACK is incompatible with Rust 2024-08-01 16:15:03 +01:00
io_uring io_uring/napi: pass ktime to io_napi_adjust_timeout 2024-07-26 08:31:59 -06:00
ipc sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +02:00
kernel Fixes and minor updates for the timer migration code: 2024-07-27 10:19:55 -07:00
lib Rust changes for v6.11 2024-07-27 13:44:54 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm mm/page_alloc: fix pcp->count race between drain_pages_zone() vs __rmqueue_pcplist() 2024-07-26 14:33:09 -07:00
net minmax: add a few more MIN_T/MAX_T users 2024-07-28 13:41:14 -07:00
rust Rust changes for v6.11 2024-07-27 13:44:54 -07:00
samples Driver core changes for 6.11-rc1 2024-07-25 10:42:22 -07:00
scripts Kbuild fixes for v6.11 2024-07-28 14:02:48 -07:00
security apparmor-pr-2024-07-24 PR 2024-07-25 2024-07-27 13:28:39 -07:00
sound Devicetree fixes for 6.11, part 1 2024-07-27 12:46:16 -07:00
tools turbostat release 2024.07.26 2024-07-28 10:52:15 -07:00
usr initramfs: shorten cmd_initfs in usr/Makefile 2024-07-16 01:07:52 +09:00
virt KVM generic changes for 6.11 2024-07-16 09:51:36 -04:00
.clang-format Docs: Move clang-format from process/ to dev-tools/ 2024-06-26 16:36:00 -06:00
.cocciconfig
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: add script and target to generate pacman package 2024-07-22 01:24:22 +09:00
.mailmap MAINTAINERS: mailmap: update James Clark's email address 2024-07-26 14:32:35 -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 tracing: Update of MAINTAINERS and CREDITS file 2024-07-18 14:08:42 -07:00
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 CXL for v6.11 merge window 2024-07-28 09:33:28 -07:00
Makefile Linux 6.11-rc1 2024-07-28 14:19:55 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -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 reStructuredText 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.