kernel/linux.git/init/Kconfig, branch v6.19.11

Merge tag 'mm-nonmm-stable-2025-12-06-11-14' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

2025-12-06T22:01:20+00:00

Pull non-MM updates from Andrew Morton: - "panic: sys_info: Refactor and fix a potential issue" (Andy Shevchenko) fixes a build issue and does some cleanup in ib/sys_info.c - "Implement mul_u64_u64_div_u64_roundup()" (David Laight) enhances the 64-bit math code on behalf of a PWM driver and beefs up the test module for these library functions - "scripts/gdb/symbols: make BPF debug info available to GDB" (Ilya Leoshkevich) makes BPF symbol names, sizes, and line numbers available to the GDB debugger - "Enable hung_task and lockup cases to dump system info on demand" (Feng Tang) adds a sysctl which can be used to cause additional info dumping when the hung-task and lockup detectors fire - "lib/base64: add generic encoder/decoder, migrate users" (Kuan-Wei Chiu) adds a general base64 encoder/decoder to lib/ and migrates several users away from their private implementations - "rbree: inline rb_first() and rb_last()" (Eric Dumazet) makes TCP a little faster - "liveupdate: Rework KHO for in-kernel users" (Pasha Tatashin) reworks the KEXEC Handover interfaces in preparation for Live Update Orchestrator (LUO), and possibly for other future clients - "kho: simplify state machine and enable dynamic updates" (Pasha Tatashin) increases the flexibility of KEXEC Handover. Also preparation for LUO - "Live Update Orchestrator" (Pasha Tatashin) is a major new feature targeted at cloud environments. Quoting the cover letter: This series introduces the Live Update Orchestrator, a kernel subsystem designed to facilitate live kernel updates using a kexec-based reboot. This capability is critical for cloud environments, allowing hypervisors to be updated with minimal downtime for running virtual machines. LUO achieves this by preserving the state of selected resources, such as memory, devices and their dependencies, across the kernel transition. As a key feature, this series includes support for preserving memfd file descriptors, which allows critical in-memory data, such as guest RAM or any other large memory region, to be maintained in RAM across the kexec reboot. Mike Rappaport merits a mention here, for his extensive review and testing work. - "kexec: reorganize kexec and kdump sysfs" (Sourabh Jain) moves the kexec and kdump sysfs entries from /sys/kernel/ to /sys/kernel/kexec/ and adds back-compatibility symlinks which can hopefully be removed one day - "kho: fixes for vmalloc restoration" (Mike Rapoport) fixes a BUG which was being hit during KHO restoration of vmalloc() regions * tag 'mm-nonmm-stable-2025-12-06-11-14' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (139 commits) calibrate: update header inclusion Reinstate "resource: avoid unnecessary lookups in find_next_iomem_res()" vmcoreinfo: track and log recoverable hardware errors kho: fix restoring of contiguous ranges of order-0 pages kho: kho_restore_vmalloc: fix initialization of pages array MAINTAINERS: TPM DEVICE DRIVER: update the W-tag init: replace simple_strtoul with kstrtoul to improve lpj_setup KHO: fix boot failure due to kmemleak access to non-PRESENT pages Documentation/ABI: new kexec and kdump sysfs interface Documentation/ABI: mark old kexec sysfs deprecated kexec: move sysfs entries to /sys/kernel/kexec test_kho: always print restore status kho: free chunks using free_page() instead of kfree() selftests/liveupdate: add kexec test for multiple and empty sessions selftests/liveupdate: add simple kexec-based selftest for LUO selftests/liveupdate: add userspace API selftests docs: add documentation for memfd preservation via LUO mm: memfd_luo: allow preserving memfd liveupdate: luo_file: add private argument to store runtime state mm: shmem: export some functions to internal.h ...

Merge tag 'drm-next-2025-12-03' of https://gitlab.freedesktop.org/drm/kernel

2025-12-04T16:53:30+00:00

Pull drm updates from Dave Airlie: "There was a rather late merge of a new color pipeline feature, that some userspace projects are blocked on, and has seen a lot of work in amdgpu. This should have seen some time in -next. There is additional support for this for Intel, that if it arrives in the next day or two I'll pass it on in another pull request and you can decide if you want to take it. Highlights: - Arm Ethos NPU accelerator driver - new DRM color pipeline support - amdgpu will now run discrete SI/CIK cards instead of radeon, which enables vulkan support in userspace - msm gets gen8 gpu support - initial Xe3P support in xe Full detail summary: New driver: - Arm Ethos-U65/U85 accel driver Core: - support the drm color pipeline in vkms/amdgfx - add support for drm colorop pipeline - add COLOR PIPELINE plane property - add DRM_CLIENT_CAP_PLANE_COLOR_PIPELINE - throttle dirty worker with vblank - use drm_for_each_bridge_in_chain_scoped in drm's bridge code - Ensure drm_client_modeset tests are enabled in UML - add simulated vblank interrupt - use in drivers - dumb buffer sizing helper - move freeing of drm client memory to driver - crtc sharpness strength property - stop using system_wq in scheduler/drivers - support emergency restore in drm-client Rust: - make slice::as_flattened usable on all supported rustc - add FromBytes::from_bytes_prefix() method - remove redundant device ptr from Rust GEM object - Change how AlwaysRefCounted is implemented for GEM objects gpuvm: - Add deferred vm_bo cleanup to GPUVM (for rust) atomic: - cleanup and improve state handling interfaces buddy: - optimize block management dma-buf: - heaps: Create heap per CMA reserved location - improve userspace documentation dp: - add POST_LT_ADJ_REQ training sequence - DPCD dSC quirk for synaptics panamera devices - helpers to query branch DSC max throughput ttm: - Rename ttm_bo_put to ttm_bo_fini - allow page protection flags on risc-v - rework pipelined eviction fence handling amdgpu: - enable amdgpu by default for SI/CI dGPUs - enable DC by default on SI - refactor CIK/SI enablement - add ABM KMS property - Re-enable DM idle optimizations - DC Analog encoders support - Powerplay fixes for fiji/iceland - Enable DC on bonaire by default - HMM cleanup - Add new RAS framework - DML2.1 updates - YCbCr420 fixes - DC FP fixes - DMUB fixes - LTTPR fixes - DTBCLK fixes - DMU cursor offload handling - Userq validation improvements - Unify shutdown callback handling - Suspend improvements - Power limit code cleanup - SR-IOV fixes - AUX backlight fixes - DCN 3.5 fixes - HDMI compliance fixes - DCN 4.0.1 cursor updates - DCN interrupt fix - DC KMS full update improvements - Add additional HDCP traces - DCN 3.2 fixes - DP MST fixes - Add support for new SR-IOV mailbox interface - UQ reset support - HDP flush rework - VCE1 support amdkfd: - HMM cleanups - Relax checks on save area overallocations - Fix GPU mappings after prefetch radeon: - refactor CIK/SI enablement xe: - Initial Xe3P support - panic support on VRAM for display - fix stolen size check - Loosen used tracking restriction - New SR-IOV debugfs structure and debugfs updates - Hide the GPU madvise flag behind a VM_BIND flag - Always expose VRAM provisioning data on discrete GPUs - Allow VRAM mappings for userptr when used with SVM - Allow pinning of p2p dma-buf - Use per-tile debugfs where appropriate - Add documentation for Execution Queues - PF improvements - VF migration recovery redesign work - User / Kernel VRAM partitioning - Update Tile-based messages - Allow configfs to disable specific GT types - VF provisioning and migration improvements - use SVM range helpers in PT layer - Initial CRI support - access VF registers using dedicated MMIO view - limit number of jobs per exec queue - add sriov_admin sysfs tree - more crescent island specific support - debugfs residency counter - SRIOV migration work - runtime registers for GFX 35 i915: - add initial Xe3p_LPD display version 35 support - Enable LNL+ content adaptive sharpness filter - Use optimized VRR guardband - Enable Xe3p LT PHY - enable FBC support for Xe3p_LPD display - add display 30.02 firmware support - refactor SKL+ watermark latency setup - refactor fbdev handling - call i915/xe runtime PM via function pointers - refactor i915/xe stolen memory/display interfaces - use display version instead of gfx version in display code - extend i915_display_info with Type-C port details - lots of display cleanups/refactorings - set O_LARGEFILE in __create_shmem - skuip guc communication warning on reset - fix time conversions - defeature DRRS on LNL+ - refactor intel_frontbuffer split between i915/xe/display - convert inteL_rom interfaces to struct drm_device - unify display register polling interfaces - aovid lock inversion when pinning to GGTT on CHV/BXT+VTD panel: - Add KD116N3730A08/A12, chromebook mt8189 - JT101TM023, LQ079L1SX01, - GLD070WX3-SL01 MIPI DSI - Samsung LTL106AL0, Samsung LTL106AL01 - Raystar RFF500F-AWH-DNN - Winstar WF70A8SYJHLNGA - Wanchanglong w552946aaa - Samsung SOFEF00 - Lenovo X13s panel - ilitek-ili9881c - add rpi 5" support - visionx-rm69299 - add backlight support - edp - support AUI B116XAN02.0 bridge: - improve ref counting - ti-sn65dsi86 - add support for DP mode with HPD - synopsis: support CEC, init timer with correct freq - ASL CS5263 DP-to-HDMI bridge support nova-core: - introduce bitfield! macro - introduce safe integer converters - GSP inits to fully booted state on Ampere - Use more future-proof register for GPU identification nova-drm: - select NOVA_CORE - 64-bit only nouveau: - improve reclocking on tegra 186+ - add large page and compression support msm: - GPU: - Gen8 support: A840 (Kaanapali) and X2-85 (Glymur) - A612 support - MDSS: - Added support for Glymur and QCS8300 platforms - DPU: - Enabled Quad-Pipe support, unlocking higher resolutions support - Added support for Glymur platform - Documented DPU on QCS8300 platform as supported - DisplayPort: - Added support for Glymur platform - Added support lame remapping inside DP block - Documented DisplayPort controller on QCS8300 and SM6150/QCS615 as supported tegra: - NVJPG driver panfrost: - display JM contexts over debugfs - export JM contexts to userspace - improve error and job handling panthor: - support custom ASN_HASH for mt8196 - support mali-G1 GPU - flush shmem write before mapping buffers uncached - make timeout per-queue instead of per-job mediatek: - MT8195/88 HDMIv2/DDCv2 support rockchip: - dsi: add support for RK3368 amdxdna: - enhance runtime PM - last hardware error reading uapi - support firmware debug output - add resource and telemetry data uapi - preemption support imx: - add driver for HDMI TX Parallel audio interface ivpu: - add support for user-managed preemption buffer - add userptr support - update JSM firware API to 3.33.0 - add better alloc/free warnings - fix page fault in unbind all bos - rework bind/unbind of imported buffers - enable MCA ECC signalling - split fw runtime and global memory buffers - add fdinfo memory statistics tidss: - convert to drm logging - logging cleanup ast: - refactor generation init paths - add per chip generation detect_tx_chip - set quirks for each chip model atmel-hlcdc: - set LCDC_ATTRE register in plane disable - set correct values for plane scaler solomon: - use drm helper for get_modes and move_valid sitronix: - fix output position when clearing screens qaic: - support dma-buf exports - support new firmware's READ_DATA implementation - sahara AIC200 image table update - add sysfs support - add coredump support - add uevents support - PM support sun4i: - layer refactors to decouple plane from output - improve DE33 support vc4: - switch to generic CEC helpers komeda: - use drm_ logging functions vkms: - configfs support for display configuration vgem: - fix fence timer deadlock etnaviv: - add HWDB entry for GC8000 Nano Ultra VIP r6205" * tag 'drm-next-2025-12-03' of https://gitlab.freedesktop.org/drm/kernel: (1869 commits) Revert "drm/amd: Skip power ungate during suspend for VPE" drm/amdgpu: use common defines for HUB faults drm/amdgpu/gmc12: add amdgpu_vm_handle_fault() handling drm/amdgpu/gmc11: add amdgpu_vm_handle_fault() handling drm/amdgpu: use static ids for ACP platform devs drm/amdgpu/sdma6: Update SDMA 6.0.3 FW version to include UMQ protected-fence fix drm/amdgpu: Forward VMID reservation errors drm/amdgpu/gmc8: Delegate VM faults to soft IRQ handler ring drm/amdgpu/gmc7: Delegate VM faults to soft IRQ handler ring drm/amdgpu/gmc6: Delegate VM faults to soft IRQ handler ring drm/amdgpu/gmc6: Cache VM fault info drm/amdgpu/gmc6: Don't print MC client as it's unknown drm/amdgpu/cz_ih: Enable soft IRQ handler ring drm/amdgpu/tonga_ih: Enable soft IRQ handler ring drm/amdgpu/iceland_ih: Enable soft IRQ handler ring drm/amdgpu/cik_ih: Enable soft IRQ handler ring drm/amdgpu/si_ih: Enable soft IRQ handler ring drm/amd/display: fix typo in display_mode_core_structs.h drm/amd/display: fix Smart Power OLED not working after S4 drm/amd/display: Move RGB-type check for audio sync to DCE HW sequence ...

Merge tag 'kbuild-6.19-1' of git://git.kernel.org/pub/scm/linux/kernel/git/kbuild/linux

2025-12-03T22:42:21+00:00

Pull Kbuild updates from Nicolas Schier: - Enable -fms-extensions, allowing anonymous use of tagged struct or union in struct/union (tag kbuild-ms-extensions-6.19). An exemplary conversion patch is added here, too (btrfs). [ Editor's note: the core of this actually came in early through a shared branch and a few other trees - Linus ] - Introduce architecture-specific CC_CAN_LINK and flags for userprogs - Add new packaging target 'modules-cpio-pkg' for building a initramfs cpio w/ kmods - Handle included .c files in gen_compile_commands - Minor kbuild changes: - Use objtree for module signing key path, fixing oot kmod signing - Improve documentation of KBUILD_BUILD_TIMESTAMP - Reuse KBUILD_USERCFLAGS for UAPI, instead of defining twice - Rename scripts/Makefile.extrawarn to Makefile.warn - Drop obsolete types.h check from headers_check.pl - Remove outdated config leak ignore entries * tag 'kbuild-6.19-1' of git://git.kernel.org/pub/scm/linux/kernel/git/kbuild/linux: kbuild: add target to build a cpio containing modules initramfs: add gen_init_cpio to hostprogs unconditionally kbuild: allow architectures to override CC_CAN_LINK init: deduplicate cc-can-link.sh invocations kbuild: don't enable CC_CAN_LINK if the dummy program generates warnings scripts: headers_install.sh: Remove two outdated config leak ignore entries scripts/clang-tools: Handle included .c files in gen_compile_commands kbuild: uapi: Drop types.h check from headers_check.pl kbuild: Rename Makefile.extrawarn to Makefile.warn MAINTAINERS, .mailmap: Update mail address for Nicolas Schier kbuild: uapi: reuse KBUILD_USERCFLAGS kbuild: doc: improve KBUILD_BUILD_TIMESTAMP documentation kbuild: Use objtree for module signing key path btrfs: send: make use of -fms-extensions for defining struct fs_path

liveupdate: kho: move to kernel/liveupdate

2025-11-27T22:24:33+00:00

Move KHO to kernel/liveupdate/ in preparation of placing all Live Update core kernel related files to the same place. [pasha.tatashin@soleen.com: disable the menu when DEFERRED_STRUCT_PAGE_INIT] Link: https://lkml.kernel.org/r/CA+CK2bAvh9Oa2SLfsbJ8zztpEjrgr_hr-uGgF1coy8yoibT39A@mail.gmail.com Link: https://lkml.kernel.org/r/20251101142325.1326536-8-pasha.tatashin@soleen.com Signed-off-by: Pasha Tatashin Reviewed-by: Jason Gunthorpe Reviewed-by: Mike Rapoport (Microsoft) Cc: Alexander Graf Cc: Changyuan Lyu Cc: Christian Brauner Cc: Jason Gunthorpe Cc: Jonathan Corbet Cc: Masahiro Yamada Cc: Miguel Ojeda Cc: Pratyush Yadav Cc: Randy Dunlap Cc: Simon Horman Cc: Tejun Heo Cc: Zhu Yanjun Signed-off-by: Andrew Morton

kbuild: allow architectures to override CC_CAN_LINK

2025-11-14T19:20:35+00:00

The generic test for CC_CAN_LINK assumes that all architectures use -m32 and -m64 to switch between 32-bit and 64-bit compilation. This is overly simplistic. Architectures may use other flags (-mabi, -m31, etc.) or may also require byte order handling (-mlittle-endian, -EL). Expressing all of the different possibilities will be very complicated and brittle. Instead allow architectures to supply their own logic which will be easy to understand and evolve. Both the boolean ARCH_HAS_CC_CAN_LINK and the string ARCH_USERFLAGS need to be implemented as kconfig does not allow the reuse of string options. Signed-off-by: Thomas Weißschuh Reviewed-by: Nicolas Schier Reviewed-by: Nathan Chancellor Link: https://patch.msgid.link/20251114-kbuild-userprogs-bits-v3-3-4dee0d74d439@linutronix.de Signed-off-by: Nicolas Schier

init: deduplicate cc-can-link.sh invocations

2025-11-14T19:20:34+00:00

The command to invoke scripts/cc-can-link.sh is very long and new usages are about to be added. Add a helper variable to make the code easier to read and maintain. Signed-off-by: Thomas Weißschuh Reviewed-by: Nicolas Schier Reviewed-by: Nathan Chancellor Link: https://patch.msgid.link/20251114-kbuild-userprogs-bits-v3-2-4dee0d74d439@linutronix.de Signed-off-by: Nicolas Schier

rust: enable slice_flatten feature and provide it through an extension trait

2025-11-14T11:25:57+00:00

In Rust 1.80, the previously unstable `slice::flatten` family of methods have been stabilized and renamed to `slice::as_flattened`. This creates an issue as we want to use `as_flattened`, but need to support the MSRV (which at the moment is Rust 1.78) where it is named `flatten`. Solve this by enabling the `slice_flatten` feature, and providing an `as_flattened` implementation through an extension trait for compiler versions where it is not available. The trait is then exported from the prelude, making the `as_flattened` family of methods transparently available for all supported compiler versions. This extension trait can be removed once the MSRV passes 1.80. Suggested-by: Miguel Ojeda Link: https://lore.kernel.org/all/CANiq72kK4pG=O35NwxPNoTO17oRcg1yfGcvr3==Fi4edr+sfmw@mail.gmail.com/ Acked-by: Danilo Krummrich Acked-by: Miguel Ojeda Reviewed-by: Alice Ryhl Signed-off-by: Alexandre Courbot Message-ID: <20251110-gsp_boot-v9-8-8ae4058e3c0e@nvidia.com> Message-ID: <20251104-b4-as-flattened-v3-1-6cb9c26b45cd@nvidia.com>

init/main.c: wrap long kernel cmdline when printing to logs

2025-11-12T18:00:16+00:00

The kernel cmdline length is allowed to be longer than what printk can handle. When this happens the cmdline that's printed to the kernel ring buffer at bootup is cutoff and some kernel cmdline options are "hidden" from the logs. This undercuts the usefulness of the log message. Specifically, grepping for COMMAND_LINE_SIZE shows that 2048 is common and some architectures even define it as 4096. s390 allows a CONFIG-based maximum up to 1MB (though it's not expected that anyone will go over the default max of 4096 [1]). The maximum message pr_notice() seems to be able to handle (based on experiment) is 1021 characters. This appears to be based on the current value of PRINTKRB_RECORD_MAX as 1024 and the fact that pr_notice() spends 2 characters on the loglevel prefix and we have a '\n' at the end. While it would be possible to increase the limits of printk() (and therefore pr_notice()) somewhat, it doesn't appear possible to increase it enough to fully include a 2048-character cmdline without breaking userspace. Specifically on at least two tested userspaces (ChromeOS plus the Debian-based distro I'm typing this message on) the `dmesg` tool reads lines from `/dev/kmsg` in 2047-byte chunks. As per `Documentation/ABI/testing/dev-kmsg`: Every read() from the opened device node receives one record of the kernel's printk buffer. ... Messages in the record ring buffer get overwritten as whole, there are never partial messages received by read(). We simply can't fit a 2048-byte cmdline plus the "Kernel command line:" prefix plus info about time/log_level/etc in a 2047-byte read. The above means that if we want to avoid the truncation we need to do some type of wrapping of the cmdline when printing. Add wrapping to the printout of the kernel command line. By default, the wrapping is set to 1021 characters to avoid breaking anyone, but allow wrapping to be set lower by a Kconfig knob "CONFIG_CMDLINE_LOG_WRAP_IDEAL_LEN". Any tools that are correctly parsing the cmdline today (because it is less than 1021 characters) will see no difference in their behavior. The format of wrapped output is designed to be matched by anyone using "grep" to search for the cmdline and also to be easy for tools to handle. Anyone who is sure their tools (if any) handle the wrapped format can choose a lower wrapping value and have prettier output. Setting CONFIG_CMDLINE_LOG_WRAP_IDEAL_LEN to 0 fully disables the wrapping logic. This means that long command lines will be truncated again, but this config could be set if command lines are expected to be long and userspace is known not to handle parsing logs with the wrapping. Wrapping is based on spaces, ignoring quotes. All lines are prefixed with "Kernel command line: " and lines that are not the last line have a " \" suffix added to them. The prefix and suffix count towards the line length for wrapping purposes. The ideal length will be exceeded if no appropriate place to wrap is found. The wrapping function added here is fairly generic and could be made a library function (somewhat like print_hex_dump()) if it's needed elsewhere in the kernel. However, having printk() directly incorporate this wrapping would be unlikely to be a good idea since it would break printouts into more than one record without any obvious common line prefix to tie lines together. It would also be extra overhead when, in general, kernel log message should simply be kept smaller than 1021 bytes. For some discussion on this topic, see responses to the v1 posting of this patch [2]. [akpm@linux-foundation.org: make print_kernel_cmdline __init] [dianders@chromium.org: v4] Link: https://lkml.kernel.org/r/20251027082204.v4.1.I095f1e2c6c27f9f4de0b4841f725f356c643a13f@changeid Link: https://lkml.kernel.org/r/20251023113257.v3.1.I095f1e2c6c27f9f4de0b4841f725f356c643a13f@changeid Link: https://lore.kernel.org/r/20251021131633.26700Dd6-hca@linux.ibm.com [1] Link: https://lore.kernel.org/r/CAD=FV=VNyt1zG_8pS64wgV8VkZWiWJymnZ-XCfkrfaAhhFSKcA@mail.gmail.com [2] Signed-off-by: Douglas Anderson Tested-by: Paul E. McKenney Cc: Alexander Shishkin Cc: Andrew Chant Cc: Brian Gerst Cc: Christian Brauner Cc: Francesco Valla Cc: Geert Uytterhoeven Cc: guoweikang Cc: Heiko Carstens Cc: Huacai Chen Cc: Ingo Molnar Cc: Jan Hendrik Farr Cc: Jeff Xu Cc: Kees Cook Cc: Masahiro Yamada Cc: Michal Koutný Cc: Miguel Ojeda Cc: Mike Rapoport Cc: Nathan Chancellor Cc: Peter Zijlstra Cc: Randy Dunlap Cc: Shakeel Butt Cc: Sven Schnelle Cc: Tejun Heo Cc: Thomas Gleinxer Signed-off-by: Andrew Morton

rseq: Switch to fast path processing on exit to user

2025-11-04T07:34:39+00:00

Now that all bits and pieces are in place, hook the RSEQ handling fast path function into exit_to_user_mode_prepare() after the TIF work bits have been handled. If case of fast path failure, TIF_NOTIFY_RESUME has been raised and the caller needs to take another turn through the TIF handling slow path. This only works for architectures which use the generic entry code. Architectures who still have their own incomplete hacks are not supported and won't be. This results in the following improvements: Kernel build Before After Reduction exit to user 80692981 80514451 signal checks: 32581 121 99% slowpath runs: 1201408 1.49% 198 0.00% 100% fastpath runs: 675941 0.84% N/A id updates: 1233989 1.53% 50541 0.06% 96% cs checks: 1125366 1.39% 0 0.00% 100% cs cleared: 1125366 100% 0 100% cs fixup: 0 0% 0 RSEQ selftests Before After Reduction exit to user: 386281778 387373750 signal checks: 35661203 0 100% slowpath runs: 140542396 36.38% 100 0.00% 100% fastpath runs: 9509789 2.51% N/A id updates: 176203599 45.62% 9087994 2.35% 95% cs checks: 175587856 45.46% 4728394 1.22% 98% cs cleared: 172359544 98.16% 1319307 27.90% 99% cs fixup: 3228312 1.84% 3409087 72.10% The 'cs cleared' and 'cs fixup' percentages are not relative to the exit to user invocations, they are relative to the actual 'cs check' invocations. While some of this could have been avoided in the original code, like the obvious clearing of CS when it's already clear, the main problem of going through TIF_NOTIFY_RESUME cannot be solved. In some workloads the RSEQ notify handler is invoked more than once before going out to user space. Doing this once when everything has stabilized is the only solution to avoid this. The initial attempt to completely decouple it from the TIF work turned out to be suboptimal for workloads, which do a lot of quick and short system calls. Even if the fast path decision is only 4 instructions (including a conditional branch), this adds up quickly and becomes measurable when the rate for actually having to handle rseq is in the low single digit percentage range of user/kernel transitions. Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Mathieu Desnoyers Link: https://patch.msgid.link/20251027084307.701201365@linutronix.de

rseq: Provide static branch for runtime debugging

2025-11-04T07:32:49+00:00

Config based debug is rarely turned on and is not available easily when things go wrong. Provide a static branch to allow permanent integration of debug mechanisms along with the usual toggles in Kconfig, command line and debugfs. Requested-by: Peter Zijlstra Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Mathieu Desnoyers Link: https://patch.msgid.link/20251027084307.089270547@linutronix.de