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Muhammad Usama Anjum 249bf97331 arm64: mte: Skip TFSR_EL1 checks and barriers in synchronous tag check mode
With KASAN_HW_TAGS (MTE) in synchronous mode, tag check faults are
reported as immediate Data Abort exceptions. The TFSR_EL1.TF1 bit is
never set since faults never go through the asynchronous path.
Therefore, reading TFSR_EL1 and executing data and instruction barriers
on kernel entry, exit, context switch and suspend is unnecessary
overhead.

As with the check_mte_async_tcf and clear_mte_async_tcf paths for
TFSRE0_EL1, extend the same optimisation to kernel entry/exit, context
switch and suspend.

All mte kselftests pass. The kunit before and after the patch show same
results.

A selection of test_vmalloc benchmarks running on a arm64 machine.
v6.19 is the baseline. (>0 is faster, <0 is slower, (R)/(I) =
statistically significant Regression/Improvement). Based on significance
and ignoring the noise, the benchmarks improved.

* 77 result classes were considered, with 9 wins, 0 losses and 68 ties

Results of fastpath [1] on v6.19 vs this patch:

+----------------------------+----------------------------------------------------------+------------+
| Benchmark                  | Result Class                                             |   barriers |
+============================+==========================================================+============+
| micromm/fork               | fork: p:1, d:10 (seconds)                                |  (I) 2.75% |
|                            | fork: p:512, d:10 (seconds)                              |      0.96% |
+----------------------------+----------------------------------------------------------+------------+
| micromm/munmap             | munmap: p:1, d:10 (seconds)                              |     -1.78% |
|                            | munmap: p:512, d:10 (seconds)                            |      5.02% |
+----------------------------+----------------------------------------------------------+------------+
| micromm/vmalloc            | fix_align_alloc_test: p:1, h:0, l:500000 (usec)          |     -0.56% |
|                            | fix_size_alloc_test: p:1, h:0, l:500000 (usec)           |      0.70% |
|                            | fix_size_alloc_test: p:4, h:0, l:500000 (usec)           |      1.18% |
|                            | fix_size_alloc_test: p:16, h:0, l:500000 (usec)          |     -5.01% |
|                            | fix_size_alloc_test: p:16, h:1, l:500000 (usec)          |     13.81% |
|                            | fix_size_alloc_test: p:64, h:0, l:100000 (usec)          |      6.51% |
|                            | fix_size_alloc_test: p:64, h:1, l:100000 (usec)          |     32.87% |
|                            | fix_size_alloc_test: p:256, h:0, l:100000 (usec)         |      4.17% |
|                            | fix_size_alloc_test: p:256, h:1, l:100000 (usec)         |      8.40% |
|                            | fix_size_alloc_test: p:512, h:0, l:100000 (usec)         |     -0.48% |
|                            | fix_size_alloc_test: p:512, h:1, l:100000 (usec)         |     -0.74% |
|                            | full_fit_alloc_test: p:1, h:0, l:500000 (usec)           |      0.53% |
|                            | kvfree_rcu_1_arg_vmalloc_test: p:1, h:0, l:500000 (usec) |     -2.81% |
|                            | kvfree_rcu_2_arg_vmalloc_test: p:1, h:0, l:500000 (usec) |     -2.06% |
|                            | long_busy_list_alloc_test: p:1, h:0, l:500000 (usec)     |     -0.56% |
|                            | pcpu_alloc_test: p:1, h:0, l:500000 (usec)               |     -0.41% |
|                            | random_size_align_alloc_test: p:1, h:0, l:500000 (usec)  |      0.89% |
|                            | random_size_alloc_test: p:1, h:0, l:500000 (usec)        |      1.71% |
|                            | vm_map_ram_test: p:1, h:0, l:500000 (usec)               |      0.83% |
+----------------------------+----------------------------------------------------------+------------+
| schbench/thread-contention | -m 16 -t 1 -r 10 -s 1000, avg_rps (req/sec)              |      0.05% |
|                            | -m 16 -t 1 -r 10 -s 1000, req_latency_p99 (usec)         |      0.60% |
|                            | -m 16 -t 1 -r 10 -s 1000, wakeup_latency_p99 (usec)      |      0.00% |
|                            | -m 16 -t 4 -r 10 -s 1000, avg_rps (req/sec)              |     -0.34% |
|                            | -m 16 -t 4 -r 10 -s 1000, req_latency_p99 (usec)         |     -0.58% |
|                            | -m 16 -t 4 -r 10 -s 1000, wakeup_latency_p99 (usec)      |      9.09% |
|                            | -m 16 -t 16 -r 10 -s 1000, avg_rps (req/sec)             |     -0.74% |
|                            | -m 16 -t 16 -r 10 -s 1000, req_latency_p99 (usec)        |     -1.40% |
|                            | -m 16 -t 16 -r 10 -s 1000, wakeup_latency_p99 (usec)     |      0.00% |
|                            | -m 16 -t 64 -r 10 -s 1000, avg_rps (req/sec)             |     -0.78% |
|                            | -m 16 -t 64 -r 10 -s 1000, req_latency_p99 (usec)        |     -0.11% |
|                            | -m 16 -t 64 -r 10 -s 1000, wakeup_latency_p99 (usec)     |      0.11% |
|                            | -m 16 -t 256 -r 10 -s 1000, avg_rps (req/sec)            |      2.64% |
|                            | -m 16 -t 256 -r 10 -s 1000, req_latency_p99 (usec)       |      3.15% |
|                            | -m 16 -t 256 -r 10 -s 1000, wakeup_latency_p99 (usec)    |     17.54% |
|                            | -m 32 -t 1 -r 10 -s 1000, avg_rps (req/sec)              |     -1.22% |
|                            | -m 32 -t 1 -r 10 -s 1000, req_latency_p99 (usec)         |      0.85% |
|                            | -m 32 -t 1 -r 10 -s 1000, wakeup_latency_p99 (usec)      |      0.00% |
|                            | -m 32 -t 4 -r 10 -s 1000, avg_rps (req/sec)              |     -0.34% |
|                            | -m 32 -t 4 -r 10 -s 1000, req_latency_p99 (usec)         |      1.05% |
|                            | -m 32 -t 4 -r 10 -s 1000, wakeup_latency_p99 (usec)      |      0.00% |
|                            | -m 32 -t 16 -r 10 -s 1000, avg_rps (req/sec)             |     -0.41% |
|                            | -m 32 -t 16 -r 10 -s 1000, req_latency_p99 (usec)        |      0.58% |
|                            | -m 32 -t 16 -r 10 -s 1000, wakeup_latency_p99 (usec)     |      2.13% |
|                            | -m 32 -t 64 -r 10 -s 1000, avg_rps (req/sec)             |      0.67% |
|                            | -m 32 -t 64 -r 10 -s 1000, req_latency_p99 (usec)        |      2.07% |
|                            | -m 32 -t 64 -r 10 -s 1000, wakeup_latency_p99 (usec)     |     -1.28% |
|                            | -m 32 -t 256 -r 10 -s 1000, avg_rps (req/sec)            |      1.01% |
|                            | -m 32 -t 256 -r 10 -s 1000, req_latency_p99 (usec)       |      0.69% |
|                            | -m 32 -t 256 -r 10 -s 1000, wakeup_latency_p99 (usec)    |     13.12% |
|                            | -m 64 -t 1 -r 10 -s 1000, avg_rps (req/sec)              |     -0.25% |
|                            | -m 64 -t 1 -r 10 -s 1000, req_latency_p99 (usec)         |     -0.48% |
|                            | -m 64 -t 1 -r 10 -s 1000, wakeup_latency_p99 (usec)      |     10.53% |
|                            | -m 64 -t 4 -r 10 -s 1000, avg_rps (req/sec)              |     -0.06% |
|                            | -m 64 -t 4 -r 10 -s 1000, req_latency_p99 (usec)         |      0.00% |
|                            | -m 64 -t 4 -r 10 -s 1000, wakeup_latency_p99 (usec)      |      0.00% |
|                            | -m 64 -t 16 -r 10 -s 1000, avg_rps (req/sec)             |     -0.36% |
|                            | -m 64 -t 16 -r 10 -s 1000, req_latency_p99 (usec)        |      0.52% |
|                            | -m 64 -t 16 -r 10 -s 1000, wakeup_latency_p99 (usec)     |      0.11% |
|                            | -m 64 -t 64 -r 10 -s 1000, avg_rps (req/sec)             |      0.52% |
|                            | -m 64 -t 64 -r 10 -s 1000, req_latency_p99 (usec)        |      3.53% |
|                            | -m 64 -t 64 -r 10 -s 1000, wakeup_latency_p99 (usec)     |     -0.10% |
|                            | -m 64 -t 256 -r 10 -s 1000, avg_rps (req/sec)            |      2.53% |
|                            | -m 64 -t 256 -r 10 -s 1000, req_latency_p99 (usec)       |      1.82% |
|                            | -m 64 -t 256 -r 10 -s 1000, wakeup_latency_p99 (usec)    |     -5.80% |
+----------------------------+----------------------------------------------------------+------------+
| syscall/getpid             | mean (ns)                                                | (I) 15.98% |
|                            | p99 (ns)                                                 | (I) 11.11% |
|                            | p99.9 (ns)                                               | (I) 16.13% |
+----------------------------+----------------------------------------------------------+------------+
| syscall/getppid            | mean (ns)                                                | (I) 14.82% |
|                            | p99 (ns)                                                 | (I) 17.86% |
|                            | p99.9 (ns)                                               |  (I) 9.09% |
+----------------------------+----------------------------------------------------------+------------+
| syscall/invalid            | mean (ns)                                                | (I) 17.78% |
|                            | p99 (ns)                                                 | (I) 11.11% |
|                            | p99.9 (ns)                                               |     13.33% |
+----------------------------+----------------------------------------------------------+------------+

[1] https://gitlab.arm.com/tooling/fastpath

Signed-off-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
History 2026-04-09 18:56:22 +01:00
arch arm64: mte: Skip TFSR_EL1 checks and barriers in synchronous tag check mode 2026-04-09 18:56:22 +01:00
block block-7.0-20260305 2026-03-06 08:36:18 -08:00
certs Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
crypto crypto: testmgr - Fix stale references to aes-generic 2026-03-03 11:57:15 -08:00
Documentation hwmon fixes for v7.0-rc3 2026-03-07 08:39:59 -08:00
drivers EFI fixes for v7.0 #2 2026-03-08 12:13:09 -07:00
fs eight client fixes 2026-03-06 16:07:22 -08:00
include eventpoll: Convert epoll_put_uevent() to scoped user access 2026-03-07 15:03:14 -08:00
init io_uring-7.0-20260305 2026-03-06 08:31:36 -08:00
io_uring io_uring-7.0-20260305 2026-03-06 08:31:36 -08:00
ipc Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
kernel Make clock_adjtime() syscall timex validation slightly more 2026-03-07 17:09:15 -08:00
lib linux_kselftest-kunit-fixes-7.0-rc3 2026-03-06 12:34:49 -08:00
LICENSES LICENSES: Add modern form of the LGPL-2.1 tags to the usage guide section 2025-10-22 07:58:19 +02:00
mm drm fixes for 7.0-rc3 2026-03-06 13:29:12 -08:00
net xdp: produce a warning when calculated tailroom is negative 2026-03-05 08:02:05 -08:00
rust linux_kselftest-kunit-fixes-7.0-rc3 2026-03-06 12:34:49 -08:00
samples USB / Thunderbolt changes for 7.0-rc1 2026-02-17 09:36:43 -08:00
scripts kbuild: install-extmod-build: Package resolve_btfids if necessary 2026-02-26 14:49:34 -07:00
security Convert remaining multi-line kmalloc_obj/flex GFP_KERNEL uses 2026-02-22 08:26:33 -08:00
sound ASoC: Fixes for v7.0 2026-03-05 17:22:14 +01:00
tools bpf-fixes 2026-03-07 12:20:37 -08:00
usr kbuild: uapi: drop dependency on CC_CAN_LINK 2026-01-16 15:02:11 -07:00
virt KVM: always define KVM_CAP_SYNC_MMU 2026-02-28 15:31:35 +01:00
.clang-format Devicetree updates for v7.0: 2026-02-11 18:27:08 -08:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig editorconfig: add rst extension 2026-01-26 19:07:09 -08:00
.get_maintainer.ignore MAINTAINERS: remove Alyssa Rosenzweig 2025-09-18 21:17:31 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: kbuild: add proc macro library support 2025-11-24 17:15:36 +01:00
.mailmap linux_kselftest-kunit-fixes-7.0-rc3 2026-03-06 12:34:49 -08:00
.pylintrc docs: Move the python libraries to tools/lib/python 2025-11-18 09:22:40 -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: remove Thomas Falcon from IBM ibmvnic 2026-03-05 07:35:45 -08:00
Kbuild sched: Make migrate_{en,dis}able() inline 2025-09-25 09:57:16 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS hwmon fixes for v7.0-rc3 2026-03-07 08:39:59 -08:00
Makefile Linux 7.0-rc3 2026-03-08 16:56:54 -07:00
README docs: add AI Coding Assistants documentation 2026-01-06 14:55:06 -07:00

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

The Linux kernel is the core of any Linux operating system. It manages hardware,
system resources, and provides the fundamental services for all other software.

Quick Start
-----------

* Report a bug: See Documentation/admin-guide/reporting-issues.rst
* Get the latest kernel: https://kernel.org
* Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst
* Join the community: https://lore.kernel.org/

Essential Documentation
-----------------------

All users should be familiar with:

* Building requirements: Documentation/process/changes.rst
* Code of Conduct: Documentation/process/code-of-conduct.rst
* License: See COPYING

Documentation can be built with make htmldocs or viewed online at:
https://www.kernel.org/doc/html/latest/


Who Are You?
============

Find your role below:

* New Kernel Developer - Getting started with kernel development
* Academic Researcher - Studying kernel internals and architecture
* Security Expert - Hardening and vulnerability analysis
* Backport/Maintenance Engineer - Maintaining stable kernels
* System Administrator - Configuring and troubleshooting
* Maintainer - Leading subsystems and reviewing patches
* Hardware Vendor - Writing drivers for new hardware
* Distribution Maintainer - Packaging kernels for distros
* AI Coding Assistant - LLMs and AI-powered development tools


For Specific Users
==================

New Kernel Developer
--------------------

Welcome! Start your kernel development journey here:

* Getting Started: Documentation/process/development-process.rst
* Your First Patch: Documentation/process/submitting-patches.rst
* Coding Style: Documentation/process/coding-style.rst
* Build System: Documentation/kbuild/index.rst
* Development Tools: Documentation/dev-tools/index.rst
* Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst
* Core APIs: Documentation/core-api/index.rst

Academic Researcher
-------------------

Explore the kernel's architecture and internals:

* Researcher Guidelines: Documentation/process/researcher-guidelines.rst
* Memory Management: Documentation/mm/index.rst
* Scheduler: Documentation/scheduler/index.rst
* Networking Stack: Documentation/networking/index.rst
* Filesystems: Documentation/filesystems/index.rst
* RCU (Read-Copy Update): Documentation/RCU/index.rst
* Locking Primitives: Documentation/locking/index.rst
* Power Management: Documentation/power/index.rst

Security Expert
---------------

Security documentation and hardening guides:

* Security Documentation: Documentation/security/index.rst
* LSM Development: Documentation/security/lsm-development.rst
* Self Protection: Documentation/security/self-protection.rst
* Reporting Vulnerabilities: Documentation/process/security-bugs.rst
* CVE Procedures: Documentation/process/cve.rst
* Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst
* Security Features: Documentation/userspace-api/seccomp_filter.rst

Backport/Maintenance Engineer
-----------------------------

Maintain and stabilize kernel versions:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* Backporting Guide: Documentation/process/backporting.rst
* Applying Patches: Documentation/process/applying-patches.rst
* Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git for Maintainers: Documentation/maintainer/configure-git.rst

System Administrator
--------------------

Configure, tune, and troubleshoot Linux systems:

* Admin Guide: Documentation/admin-guide/index.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst
* Tracing/Debugging: Documentation/trace/index.rst
* Performance Security: Documentation/admin-guide/perf-security.rst
* Hardware Monitoring: Documentation/hwmon/index.rst

Maintainer
----------

Lead kernel subsystems and manage contributions:

* Maintainer Handbook: Documentation/maintainer/index.rst
* Pull Requests: Documentation/maintainer/pull-requests.rst
* Managing Patches: Documentation/maintainer/modifying-patches.rst
* Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst
* Development Process: Documentation/process/maintainer-handbooks.rst
* Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git Configuration: Documentation/maintainer/configure-git.rst

Hardware Vendor
---------------

Write drivers and support new hardware:

* Driver API Guide: Documentation/driver-api/index.rst
* Driver Model: Documentation/driver-api/driver-model/driver.rst
* Device Drivers: Documentation/driver-api/infrastructure.rst
* Bus Types: Documentation/driver-api/driver-model/bus.rst
* Device Tree Bindings: Documentation/devicetree/bindings/
* Power Management: Documentation/driver-api/pm/index.rst
* DMA API: Documentation/core-api/dma-api.rst

Distribution Maintainer
-----------------------

Package and distribute the kernel:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* ABI Documentation: Documentation/ABI/README
* Kernel Configuration: Documentation/kbuild/kconfig.rst
* Module Signing: Documentation/admin-guide/module-signing.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst

AI Coding Assistant
-------------------

CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and
follow the AI coding assistants documentation before contributing to the Linux
kernel:

* Documentation/process/coding-assistants.rst

This documentation contains essential requirements about licensing, attribution,
and the Developer Certificate of Origin that all AI tools must comply with.


Communication and Support
=========================

* Mailing Lists: https://lore.kernel.org/
* IRC: #kernelnewbies on irc.oftc.net
* Bugzilla: https://bugzilla.kernel.org/
* MAINTAINERS file: Lists subsystem maintainers and mailing lists
* Email Clients: Documentation/process/email-clients.rst