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
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Pull x86 fixes from Ingo Molnar:
- Fix speculative safety in fred_extint()
- Fix __WARN_printf() trap in early_fixup_exception()
- Fix clang-build boot bug for unusual alignments, triggered by
CONFIG_DEBUG_FORCE_FUNCTION_ALIGN_64B=y
- Replace the final few __ASSEMBLY__ stragglers that snuck in lately
into non-UAPI x86 headers and use __ASSEMBLER__ consistently (again)
* tag 'x86-urgent-2026-03-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/headers: Replace __ASSEMBLY__ stragglers with __ASSEMBLER__
x86/cfi: Fix CFI rewrite for odd alignments
x86/bug: Handle __WARN_printf() trap in early_fixup_exception()
x86/fred: Correct speculative safety in fred_extint()
Pull timer fix from Ingo Molnar:
"Improve the inlining of jiffies_to_msecs() and jiffies_to_usecs(), for
the common HZ=100, 250 or 1000 cases. Only use a function call for odd
HZ values like HZ=300 that generate more code.
The function call overhead showed up in performance tests of the TCP
code"
* tag 'timers-urgent-2026-03-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
time/jiffies: Inline jiffies_to_msecs() and jiffies_to_usecs()
After converting the __ASSEMBLY__ statements to __ASSEMBLER__ in
commit 24a295e4ef1ca ("x86/headers: Replace __ASSEMBLY__ with
__ASSEMBLER__ in non-UAPI headers"), some new code has been
added that uses __ASSEMBLY__ again. Convert these stragglers, too.
This is a mechanical patch, done with a simple "sed -i" command.
Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251218182029.166993-1-thuth@redhat.com
Pull scheduler fixes from Ingo Molnar:
- Fix zero_vruntime tracking when there's a single task running
- Fix slice protection logic
- Fix the ->vprot logic for reniced tasks
- Fix lag clamping in mixed slice workloads
- Fix objtool uaccess warning (and bug) in the
!CONFIG_RSEQ_SLICE_EXTENSION case caused by unexpected un-inlining,
which triggers with older compilers
- Fix a comment in the rseq registration rseq_size bound check code
- Fix a legacy RSEQ ABI quirk that handled 32-byte area sizes
differently, which special size we now reached naturally and want to
avoid. The visible ugliness of the new reserved field will be avoided
the next time the RSEQ area is extended.
* tag 'sched-urgent-2026-03-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
rseq: slice ext: Ensure rseq feature size differs from original rseq size
rseq: Clarify rseq registration rseq_size bound check comment
sched/core: Fix wakeup_preempt's next_class tracking
rseq: Mark rseq_arm_slice_extension_timer() __always_inline
sched/fair: Fix lag clamp
sched/eevdf: Update se->vprot in reweight_entity()
sched/fair: Only set slice protection at pick time
sched/fair: Fix zero_vruntime tracking
For common cases (HZ=100, 250 or 1000), these helpers are at most one
multiply, so there is no point calling a tiny function.
Keep them out of line for HZ=300 and others.
This saves cycles in TCP fast path, among other things.
$ scripts/bloat-o-meter -t vmlinux.old vmlinux.new
add/remove: 0/8 grow/shrink: 25/89 up/down: 530/-3474 (-2944)
...
nla_put_msecs 193 - -193
message_stats_print 2131 920 -1211
Total: Before=25365208, After=25362264, chg -0.01%
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260210170226.57209-1-edumazet@google.com
Rustam reported his clang builds did not boot properly; turns out his
.config has: CONFIG_DEBUG_FORCE_FUNCTION_ALIGN_64B=y set.
Fix up the FineIBT code to deal with this unusual alignment.
Fixes: 931ab63664f0 ("x86/ibt: Implement FineIBT")
Reported-by: Rustam Kovhaev <rkovhaev@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Rustam Kovhaev <rkovhaev@gmail.com>
Pull perf events fixes from Ingo Molnar:
- Fix lock ordering bug found by lockdep in perf_event_wakeup()
- Fix uncore counter enumeration on Granite Rapids and Sierra Forest
- Fix perf_mmap() refcount bug found by Syzkaller
- Fix __perf_event_overflow() vs perf_remove_from_context() race
* tag 'perf-urgent-2026-03-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
perf: Fix __perf_event_overflow() vs perf_remove_from_context() race
perf/core: Fix refcount bug and potential UAF in perf_mmap
perf/x86/intel/uncore: Add per-scheduler IMC CAS count events
perf/core: Fix invalid wait context in ctx_sched_in()
Before rseq became extensible, its original size was 32 bytes even
though the active rseq area was only 20 bytes. This had the following
impact in terms of userspace ecosystem evolution:
* The GNU libc between 2.35 and 2.39 expose a __rseq_size symbol set
to 32, even though the size of the active rseq area is really 20.
* The GNU libc 2.40 changes this __rseq_size to 20, thus making it
express the active rseq area.
* Starting from glibc 2.41, __rseq_size corresponds to the
AT_RSEQ_FEATURE_SIZE from getauxval(3).
This means that users of __rseq_size can always expect it to
correspond to the active rseq area, except for the value 32, for
which the active rseq area is 20 bytes.
Exposing a 32 bytes feature size would make life needlessly painful
for userspace. Therefore, add a reserved field at the end of the
rseq area to bump the feature size to 33 bytes. This reserved field
is expected to be replaced with whatever field will come next,
expecting that this field will be larger than 1 byte.
The effect of this change is to increase the size from 32 to 64 bytes
before we actually have fields using that memory.
Clarify the allocation size and alignment requirements in the struct
rseq uapi comment.
Change the value returned by getauxval(AT_RSEQ_ALIGN) to return the
value of the active rseq area size rounded up to next power of 2, which
guarantees that the rseq structure will always be aligned on the nearest
power of two large enough to contain it, even as it grows. Change the
alignment check in the rseq registration accordingly.
This will minimize the amount of ABI corner-cases we need to document
and require userspace to play games with. The rule stays simple when
__rseq_size != 32:
#define rseq_field_available(field) (__rseq_size >= offsetofend(struct rseq_abi, field))
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260220200642.1317826-3-mathieu.desnoyers@efficios.com
Pull powerpc updates for 7.0
- Implement masked user access
- Add bpf support for internal only per-CPU instructions and inline the
bpf_get_smp_processor_id() and bpf_get_current_task() functions
- Fix pSeries MSI-X allocation failure when quota is exceeded
- Fix recursive pci_lock_rescan_remove locking in EEH event handling
- Support tailcalls with subprogs & BPF exceptions on 64bit
- Extend "trusted" keys to support the PowerVM Key Wrapping Module
(PKWM)
Thanks to Abhishek Dubey, Christophe Leroy, Gaurav Batra, Guangshuo Li,
Jarkko Sakkinen, Mahesh Salgaonkar, Mimi Zohar, Miquel Sabaté Solà, Nam
Cao, Narayana Murty N, Nayna Jain, Nilay Shroff, Puranjay Mohan, Saket
Kumar Bhaskar, Sourabh Jain, Srish Srinivasan, and Venkat Rao Bagalkote.
* tag 'powerpc-7.0-1' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux: (27 commits)
powerpc/pseries: plpks: export plpks_wrapping_is_supported
docs: trusted-encryped: add PKWM as a new trust source
keys/trusted_keys: establish PKWM as a trusted source
pseries/plpks: add HCALLs for PowerVM Key Wrapping Module
pseries/plpks: expose PowerVM wrapping features via the sysfs
powerpc/pseries: move the PLPKS config inside its own sysfs directory
pseries/plpks: fix kernel-doc comment inconsistencies
powerpc/smp: Add check for kcalloc() failure in parse_thread_groups()
powerpc: kgdb: Remove OUTBUFMAX constant
powerpc64/bpf: Additional NVR handling for bpf_throw
powerpc64/bpf: Support exceptions
powerpc64/bpf: Add arch_bpf_stack_walk() for BPF JIT
powerpc64/bpf: Avoid tailcall restore from trampoline
powerpc64/bpf: Support tailcalls with subprogs
powerpc64/bpf: Moving tail_call_cnt to bottom of frame
powerpc/eeh: fix recursive pci_lock_rescan_remove locking in EEH event handling
powerpc/pseries: Fix MSI-X allocation failure when quota is exceeded
powerpc/iommu: bypass DMA APIs for coherent allocations for pre-mapped memory
powerpc64/bpf: Inline bpf_get_smp_processor_id() and bpf_get_current_task/_btf()
powerpc64/bpf: Support internal-only MOV instruction to resolve per-CPU addrs
...
The commit 5b472b6e5bd9 ("x86_64/bug: Implement __WARN_printf()")
implemented __WARN_printf(), which changed the mechanism to use UD1
instead of UD2. However, it only handles the trap in the runtime IDT
handler, while the early booting IDT handler lacks this handling. As a
result, the usage of WARN() before the runtime IDT setup can lead to
kernel crashes. Since KMSAN is enabled after the runtime IDT setup, it
is safe to use handle_bug() directly in early_fixup_exception() to
address this issue.
Fixes: 5b472b6e5bd9 ("x86_64/bug: Implement __WARN_printf()")
Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/c4fb3645f60d3a78629d9870e8fcc8535281c24f.1768016713.git.houwenlong.hwl@antgroup.com
Pull locking fix from Ingo Molnar:
"Now that LLVM 22 has been released officially, require a release
version to use the new CONFIG_WARN_CONTEXT_ANALYSIS feature.
In particular this avoids the widely used Android clang 22.0.1
pre-release build which is known to be broken for this usecase"
* tag 'locking-urgent-2026-03-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
lib/Kconfig.debug: Require a release version of LLVM 22 for context analysis
Make sure that __perf_event_overflow() runs with IRQs disabled for all
possible callchains. Specifically the software events can end up running
it with only preemption disabled.
This opens up a race vs perf_event_exit_event() and friends that will go
and free various things the overflow path expects to be present, like
the BPF program.
Fixes: 592903cdcbf6 ("perf_counter: add an event_list")
Reported-by: Simond Hu <cmdhh1767@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Simond Hu <cmdhh1767@gmail.com>
Link: https://patch.msgid.link/20260224122909.GV1395416@noisy.programming.kicks-ass.net
The rseq registration validates that the rseq_size argument is greater
or equal to 32 (the original rseq size), but the comment associated with
this check does not clearly state this.
Clarify the comment to that effect.
Fixes: ee3e3ac05c26 ("rseq: Introduce extensible rseq ABI")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260220200642.1317826-2-mathieu.desnoyers@efficios.com
Pull parisc updates from Helge Deller:
- Fix device reference leak in error path
- Check if system provides a 64-bit free running platform counter
- Minor fixes in debug code
* tag 'parisc-for-7.0-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux:
parisc: lba_pci: Add debug code to show IO and PA ranges
parisc: Detect 64-bit free running platform counter
parisc: Fix minor printk issues in iosapic debug code
parisc: Enhance debug code for PAT firmware
parisc: Add PDC PAT call to get free running 64-bit counter
parisc: Fix module path output in qemu tables
parisc: Export model name for MPE/ix
parisc: Prevent interrupts during reboot
parisc: Print hardware IDs as 4 digit hex strings
parisc: kernel: replace kfree() with put_device() in create_tree_node()
Building trusted-keys as a module fails modpost with:
ERROR: modpost: "plpks_wrapping_is_supported" [security/keys/trusted-keys/
trusted.ko] undefined!
Export plpks_wrapping_is_supported() so trusted-keys links cleanly
This patch is intended to be applied on top of the earlier "Extend "trusted
" keys to support a new trust source named the PowerVM Key Wrapping Module
(PKWM)" series (v5).
Link: https://lore.kernel.org/all/20260127145228.48320-1-ssrish@linux.ibm.com/
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202602010724.1g9hbLKv-lkp@intel.com/
Signed-off-by: Srish Srinivasan <ssrish@linux.ibm.com>
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260201165344.950870-1-ssrish@linux.ibm.com
array_index_nospec() is no use if the result gets spilled to the stack, as
it makes the believed safe-under-speculation value subject to memory
predictions.
For all practical purposes, this means array_index_nospec() must be used in
the expression that accesses the array.
As the code currently stands, it's the wrong side of irqentry_enter(), and
'index' is put into %ebp across the function call.
Remove the index variable and reposition array_index_nospec(), so it's
calculated immediately before the array access.
Fixes: 14619d912b65 ("x86/fred: FRED entry/exit and dispatch code")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260106131504.679932-1-andrew.cooper3@citrix.com