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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The active_req field serves double duty as both the "is a TX in
flight" flag (NULL means idle) and the storage for the in-flight
message pointer. When a client sends NULL via mbox_send_message(),
active_req is set to NULL, which the framework misinterprets as
"no active request". This breaks the TX state machine by:
- tx_tick() short-circuits on (!mssg), skipping the tx_done
callback and the tx_complete completion
- txdone_hrtimer() skips the channel entirely since active_req
is NULL, so poll-based TX-done detection never fires.
Fix this by introducing a MBOX_NO_MSG sentinel value that means
"no active request," freeing NULL to be valid message data. The
sentinel is defined in the subsystem-internal mailbox.h so that
controller drivers within drivers/mailbox/ can reference it, but
it is not exposed to clients outside the subsystem.
Fifteen in-tree callers send NULL (doorbell-style IPCs on Qualcomm,
Tegra, TI, Xilinx, i.MX, SCMI, and PCC platforms). All were
audited for regression:
- Most already work around the bug via knows_txdone=true with a
manual mbox_client_txdone() call, making the framework's
tracking irrelevant. These are unaffected.
- Poll-based callers (Xilinx zynqmp/r5) are strictly better off:
the poll timer now correctly detects NULL-active channels
instead of silently skipping them.
- irq-qcom-mpm.c was a pre-existing bug -- the only Qualcomm
caller that omitted the knows_txdone + mbox_client_txdone()
pattern. Fixed in a companion commit ("irqchip/qcom-mpm: Fix
missing mailbox TX done acknowledgment").
- No caller sets both a tx_done callback and sends NULL, nor
combines tx_block=true with NULL sends, so the newly reachable
callback/completion paths are never exercised.
Also update tegra-hsp's flush callback, which directly inspects
active_req to wait for the channel to drain: the old "!= NULL"
check becomes "!= MBOX_NO_MSG", otherwise flush spins until
timeout since the sentinel is non-NULL.
The only tradeoff is that 'MBOX_NO_MSG' can not be used as a message
by clients.
Reported-by: Joonwon Kang <joonwonkang@google.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>
Quite some controller drivers use the defines from the internal header
already. This prevents controller drivers outside the mailbox directory.
Move the defines to the public controller header to allow this again as
the defines are not strictly internal anyhow.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Sudeep Holla <sudeep.holla@kernel.org>
Reviewed-by: Daniel Baluta <daniel.baluta@nxp.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>
"Request" is wrong, there is a separate function for requesting. This
functions binds, so describe this.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>
Memory resources are optional but if the resource is empty
devm_platform_get_and_ioremap_resource() prints an error nonetheless.
Refactor the code to check the resources locally first and process them
only if they are present. The -EBUSY error message of ioremap_resource()
is still kept because it is correct. The comment which explains that a
plain ioremap() is tried as a workaround is turned into a info message.
So, a user will be informed about it, too.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>
The core initializes the 'mbox' field exactly like this, so don't
duplicate it in the driver.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Tested-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>
Fix CURR and END address calculation for inserting a cmdq task into the
task list by using cmdq_reg_shift_addr() for proper address converting.
This ensures both CURR and END addresses are set correctly when
enabling the thread.
Fixes: a195c7ccfb7a ("mailbox: mtk-cmdq: Refine DMA address handling for the command buffer")
Signed-off-by: Jason-JH Lin <jason-jh.lin@mediatek.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>
The return value of mtk_vcp_mbox_xlate() is checked by IS_ERR(), so
return NULL is incorrect and could lead to a NULL pointer dereference.
Fixes: b562abd95672 ("mailbox: mediatek: Add mtk-vcp-mailbox driver")
Signed-off-by: Felix Gu <ustc.gu@gmail.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>
Reduce allocations to a single one by using a flexible array member.
Allows using __counted_by for extra runtime analysis.
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>
Use a flexible array member to reduce allocations.
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>
Clients sometimes need to know whether the mailbox TX queue has room
before posting a new message. Rather than exposing internal queue state
through a struct field, provide a proper accessor function that returns
the number of available slots for a given channel.
This lets clients choose to back off when the queue is full instead of
hitting the -ENOBUFS error path and the misleading "Try increasing
MBOX_TX_QUEUE_LEN" warning.
Tested-by: Tanmay Shah <tanmay.shah@amd.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>
Pull kvm fixes from Paolo Bonzini:
"Arm:
- Make sure we don't leak any S1POE state from guest to guest when
the feature is supported on the HW, but not enabled on the host
- Propagate the ID registers from the host into non-protected VMs
managed by pKVM, ensuring that the guest sees the intended feature
set
- Drop double kern_hyp_va() from unpin_host_sve_state(), which could
bite us if we were to change kern_hyp_va() to not being idempotent
- Don't leak stage-2 mappings in protected mode
- Correctly align the faulting address when dealing with single page
stage-2 mappings for PAGE_SIZE > 4kB
- Fix detection of virtualisation-capable GICv5 IRS, due to the
maintainer being obviously fat fingered... [his words, not mine]
- Remove duplication of code retrieving the ASID for the purpose of
S1 PT handling
- Fix slightly abusive const-ification in vgic_set_kvm_info()
Generic:
- Remove internal Kconfigs that are now set on all architectures
- Remove per-architecture code to enable KVM_CAP_SYNC_MMU, all
architectures finally enable it in Linux 7.0"
* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm:
KVM: always define KVM_CAP_SYNC_MMU
KVM: remove CONFIG_KVM_GENERIC_MMU_NOTIFIER
KVM: arm64: Deduplicate ASID retrieval code
irqchip/gic-v5: Fix inversion of IRS_IDR0.virt flag
KVM: arm64: Revert accidental drop of kvm_uninit_stage2_mmu() for non-NV VMs
KVM: arm64: Fix protected mode handling of pages larger than 4kB
KVM: arm64: vgic: Handle const qualifier from gic_kvm_info allocation type
KVM: arm64: Remove redundant kern_hyp_va() in unpin_host_sve_state()
KVM: arm64: Fix ID register initialization for non-protected pKVM guests
KVM: arm64: Optimise away S1POE handling when not supported by host
KVM: arm64: Hide S1POE from guests when not supported by the host
Pull debugobjects fix from Thomas Gleixner:
"A single fix for debugobjects.
The deferred page initialization prevents debug objects from
allocating slab pages until the initialization is complete. That
causes depletion of the pool and disabling of debugobjects.
The reason is that debugobjects uses __GFP_HIGH for allocations as it
might be invoked from arbitrary contexts. When PREEMPT_COUNT is
disabled there is no way to know whether the context is safe to set
__GFP_KSWAPD_RECLAIM.
This worked until v6.18. Since then allocations w/o a reclaim flag
cause new_slab() to end up in alloc_frozen_pages_nolock_noprof(),
which returns early when deferred page initialization has not yet
completed.
Work around that when PREEMPT_COUNT is enabled as the preempt counter
allows debugobjects to add __GFP_KSWAPD_RECLAIM to the GFP flags when
the context is preemtible. When PREEMPT_COUNT is disabled the context
is unknown and the reclaim bit can't be set because the caller might
hold locks which might deadlock in the allocator.
That makes debugobjects depend on PREEMPT_COUNT ||
!DEFERRED_STRUCT_PAGE_INIT, which limits the coverage slightly, but
keeps it functional for most cases"
* tag 'core-debugobjects-2026-03-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
debugobject: Make it work with deferred page initialization - again
KVM/arm64 fixes for 7.0, take #1
- Make sure we don't leak any S1POE state from guest to guest when
the feature is supported on the HW, but not enabled on the host
- Propagate the ID registers from the host into non-protected VMs
managed by pKVM, ensuring that the guest sees the intended feature set
- Drop double kern_hyp_va() from unpin_host_sve_state(), which could
bite us if we were to change kern_hyp_va() to not being idempotent
- Don't leak stage-2 mappings in protected mode
- Correctly align the faulting address when dealing with single page
stage-2 mappings for PAGE_SIZE > 4kB
- Fix detection of virtualisation-capable GICv5 IRS, due to the
maintainer being obviously fat fingered...
- Remove duplication of code retrieving the ASID for the purpose of
S1 PT handling
- Fix slightly abusive const-ification in vgic_set_kvm_info()
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()
debugobjects uses __GFP_HIGH for allocations as it might be invoked
within locked regions. That worked perfectly fine until v6.18. It still
works correctly when deferred page initialization is disabled and works
by chance when no page allocation is required before deferred page
initialization has completed.
Since v6.18 allocations w/o a reclaim flag cause new_slab() to end up in
alloc_frozen_pages_nolock_noprof(), which returns early when deferred
page initialization has not yet completed. As the deferred page
initialization takes quite a while the debugobject pool is depleted and
debugobjects are disabled.
This can be worked around when PREEMPT_COUNT is enabled as that allows
debugobjects to add __GFP_KSWAPD_RECLAIM to the GFP flags when the context
is preemtible. When PREEMPT_COUNT is disabled the context is unknown and
the reclaim bit can't be set because the caller might hold locks which
might deadlock in the allocator.
In preemptible context the reclaim bit is harmless and not a performance
issue as that's usually invoked from slow path initialization context.
That makes debugobjects depend on PREEMPT_COUNT || !DEFERRED_STRUCT_PAGE_INIT.
Fixes: af92793e52c3 ("slab: Introduce kmalloc_nolock() and kfree_nolock().")
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Link: https://patch.msgid.link/87pl6gznti.ffs@tglx
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