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Puranjay Mohan says: ==================== Remove KF_SLEEPABLE from arena kfuncs V7: https://lore.kernel.org/all/20251222190815.4112944-1-puranjay@kernel.org/ Changes in V7->v8: - Use clear_lo32(arena->user_vm_start) in place of user_vm_start in patch 3 V6: https://lore.kernel.org/all/20251217184438.3557859-1-puranjay@kernel.org/ Changes in v6->v7: - Fix a deadlock in patch 1, that was being fixed in patch 2. Move the fix to patch 1. - Call flush_cache_vmap() after setting up the mappings as it is required by some architectures. V5: https://lore.kernel.org/all/20251212044516.37513-1-puranjay@kernel.org/ Changes in v5->v6: Patch 1: - Add a missing ; to make sure this patch builds individually. (AI) V4: https://lore.kernel.org/all/20251212004350.6520-1-puranjay@kernel.org/ Changes in v4->v5: Patch 1: - Fix a memory leak in arena_alloc_pages(), it was being fixed in Patch 3 but, every patch should be complete in itself. (AI) Patch 3: - Don't do useless addition in arena_alloc_pages() (Alexei) - Add a comment about kmalloc_nolock() failure and expectations. v3: https://lore.kernel.org/all/20251117160150.62183-1-puranjay@kernel.org/ Changes in v3->v4: - Coding style changes related to comments in Patch 2/3 (Alexei) v2: https://lore.kernel.org/all/20251114111700.43292-1-puranjay@kernel.org/ Changes in v2->v3: Patch 1: - Call range_tree_destroy() in error path of populate_pgtable_except_pte() in arena_map_alloc() (AI) Patch 2: - Fix double mutex_unlock() in the error path of arena_alloc_pages() (AI) - Fix coding style issues (Alexei) Patch 3: - Unlock spinlock before returning from arena_vm_fault() in case BPF_F_SEGV_ON_FAULT is set by user. (AI) - Use __llist_del_all() in place of llist_del_all for on-stack llist (free_pages) (Alexei) - Fix build issues on 32-bit systems where arena.c is not compiled. (kernel test robot) - Make bpf_arena_alloc_pages() polymorphic so it knows if it has been called in sleepable or non-sleepable context. This information is passed to arena_free_pages() in the error path. Patch 4: - Add a better comment for the big_alloc3() test that triggers kmalloc_nolock()'s limit and if bpf_arena_alloc_pages() works correctly above this limit. v1: https://lore.kernel.org/all/20251111163424.16471-1-puranjay@kernel.org/ Changes in v1->v2: Patch 1: - Import tlbflush.h to fix build issue in loongarch. (kernel test robot) - Fix unused variable error in apply_range_clear_cb() (kernel test robot) - Call bpf_map_area_free() on error path of populate_pgtable_except_pte() (AI) - Use PAGE_SIZE in apply_to_existing_page_range() (AI) Patch 2: - Cap allocation made by kmalloc_nolock() for pages array to KMALLOC_MAX_CACHE_SIZE and reuse the array in an explicit loop to overcome this limit. (AI) Patch 3: - Do page_ref_add(page, 1); under the spinlock to mitigate a race (AI) Patch 4: - Add a new testcase big_alloc3() verifier_arena_large.c that tries to allocate a large number of pages at once, this is to trigger the kmalloc_nolock() limit in Patch 2 and see if the loop logic works correctly. This set allows arena kfuncs to be called from non-sleepable contexts. It is acheived by the following changes: The range_tree is now protected with a rqspinlock and not a mutex, this change is enough to make bpf_arena_reserve_pages() any context safe. bpf_arena_alloc_pages() had four points where it could sleep: 1. Mutex to protect range_tree: now replaced with rqspinlock 2. kvcalloc() for allocations: now replaced with kmalloc_nolock() 3. Allocating pages with bpf_map_alloc_pages(): this already calls alloc_pages_nolock() in non-sleepable contexts and therefore is safe. 4. Setting up kernel page tables with vm_area_map_pages(): vm_area_map_pages() may allocate memory while inserting pages into bpf arena's vm_area. Now, at arena creation time populate all page table levels except the last level and when new pages need to be inserted call apply_to_page_range() again which will only do set_pte_at() for those pages and will not allocate memory. The above four changes make bpf_arena_alloc_pages() any context safe. bpf_arena_free_pages() has to do the following steps: 1. Update the range_tree 2. vm_area_unmap_pages(): to unmap pages from kernel vm_area 3. flush the tlb: done in step 2, already. 4. zap_pages(): to unmap pages from user page tables 5. free pages. The third patch in this set makes bpf_arena_free_pages() polymorphic using the specialize_kfunc() mechanism. When called from a sleepable context, arena_free_pages() remains mostly unchanged except the following: 1. rqspinlock is taken now instead of the mutex for the range tree 2. Instead of using vm_area_unmap_pages() that can free intermediate page table levels, apply_to_existing_page_range() with a callback is used that only does pte_clear() on the last level and leaves the intermediate page table levels intact. This is needed to make sure that bpf_arena_alloc_pages() can safely do set_pte_at() without allocating intermediate page tables. When arena_free_pages() is called from a non-sleepable context or it fails to acquire the rqspinlock in the sleepable case, a lock-less list of struct arena_free_span is used to queue the uaddr and page cnt. kmalloc_nolock() is used to allocate this arena_free_span, this can fail but we need to make this trade-off for frees done from non-sleepable contexts. arena_free_pages() then raises an irq_work whose handler in turn schedules work that iterate this list and clears ptes, flushes tlbs, zap pages, and frees pages for the queued uaddr and page cnts. apply_range_clear_cb() with apply_to_existing_page_range() is used to clear PTEs and collect pages to be freed, struct llist_node pcp_llist; in the struct page is used to do this. ==================== Link: https://patch.msgid.link/20251222195022.431211-1-puranjay@kernel.org Signed-off-by: Alexei Starovoitov <ast@kernel.org> |
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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 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 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