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microblaze handles TLB misses in software, and the handler builds the address of the L1 entry by ORing the index into the page directory base instead of adding it (hw_exception_handler.S): bsrli r5, r3, PGDIR_SHIFT - 2 andi r5, r5, PAGE_SIZE - 4 /* Assume pgdir aligned on 4K boundary, no need for "andi r4,r4,0xfffff003" */ or r4, r4, r5 lwi r4, r4, 0 /* Get L1 entry */ The index is masked to the low 12 bits, so the OR only works if those bits of the base are zero -- which is exactly the assumption the comment states and the reason the masking of the base can be skipped. swapper_pg_dir had no alignment directive of its own. It was aligned because it followed empty_zero_page in head.S, and that one carried the .align 12: .section .data .global empty_zero_page .align 12 empty_zero_page: .space PAGE_SIZE .global swapper_pg_dir swapper_pg_dir: .space PAGE_SIZE Commit6215d9f447("arch, mm: consolidate empty_zero_page") removed empty_zero_page from head.S, and with it the .align 12 that -- despite sitting next to empty_zero_page -- was what page aligned swapper_pg_dir. Since then swapper_pg_dir lands wherever .data happens to put it, its low bits are no longer zero, and every kernel TLB miss ORs the index into a base with a nonzero offset. The resulting L1 lookups read the wrong words, no valid translation is ever installed, and the kernel spins in exceptions long before it can print anything. On qemu-system-microblazeel (petalogix-s3adsp1800) the console stays completely silent at 100% CPU; there is no oops and no guest error reported by qemu, which makes this awkward to diagnose. Give swapper_pg_dir the alignment it requires, rather than relying on a neighbour to provide it. microblaze has no noMMU variant left in mainline -- CONFIG_MMU is def_bool y and mmu_defconfig is the only defconfig -- so this is not a corner case: every mainline microblaze kernel since v7.1-rc1 fails to boot, including the v7.1 release. v7.0: swapper_pg_dir = 0xc05fd000 (aligned) v7.1-rc1: swapper_pg_dir = 0xc0603140 (offset 320) v7.1-rc1 + this fix: swapper_pg_dir = 0xc0604000 (aligned) next-20260726: swapper_pg_dir = 0xc0615140 (offset 320) next-20260726 + this fix: swapper_pg_dir = 0xc0616000 (aligned) Verified on qemu-system-microblazeel (petalogix-s3adsp1800) with mmu_defconfig and microblazeel gcc 12.5.0: v7.1-rc1 and next-20260726 both print nothing at all without the fix, and both boot to userspace with it. Link: https://lore.kernel.org/20260727215823.1422701-1-ramin.moussavi@yacoub.de Fixes:6215d9f447("arch, mm: consolidate empty_zero_page") Signed-off-by: Ramin Moussavi <ramin.moussavi@yacoub.de> Cc: Michal Simek <monstr@monstr.eu> Cc: Mike Rapoport <rppt@kernel.org> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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