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Skip processing hugepage kernel arguments (hugepagesz, hugepages, and
default_hugepagesz) when hugepages are not supported by the architecture.
Some architectures may need to disable hugepages based on conditions
discovered during kernel boot. The hugepages_supported() helper allows
architecture code to advertise whether hugepages are supported.
Currently, normal hugepage allocation is guarded by hugepages_supported(),
but gigantic hugepages are allocated regardless of this check. This
causes problems on powerpc for fadump (firmware- assisted dump).
In the fadump (firmware-assisted dump) scenario, a production kernel crash
causes the system to boot into a special kernel whose sole purpose is to
collect the memory dump and reboot. Features such as hugepages are not
required in this environment and should be disabled.
For example, when the fadump kernel boots with the following kernel
arguments:
default_hugepagesz=1GB hugepagesz=1GB hugepages=200
Before this patch, the kernel prints the following logs:
HugeTLB: allocating 200 of page size 1.00 GiB failed. Only allocated 58 hugepages.
HugeTLB support is disabled!
HugeTLB: huge pages not supported, ignoring associated command-line parameters
hugetlbfs: disabling because there are no supported hugepage sizes
Even though the logs state that HugeTLB support is disabled, gigantic
hugepages are still allocated. This causes the fadump kernel to run out
of memory during boot.
After this patch is applied, the kernel prints the following logs for
the same command line:
HugeTLB: hugepages unsupported, ignoring default_hugepagesz=1GB cmdline
HugeTLB: hugepages unsupported, ignoring hugepagesz=1GB cmdline
HugeTLB: hugepages unsupported, ignoring hugepages=200 cmdline
HugeTLB support is disabled!
hugetlbfs: disabling because there are no supported hugepage sizes
To fix the issue, gigantic hugepage allocation should be guarded by
hugepages_supported().
Previously, two approaches were proposed to bring gigantic hugepage
allocation under hugepages_supported():
[1] Check hugepages_supported() in the generic code before allocating
gigantic hugepages
[2] Make arch_hugetlb_valid_size() return false for all hugetlb sizes
Approach [2] has two minor issues:
1. It prints misleading logs about invalid hugepage sizes
2. The kernel still processes hugepage kernel arguments unnecessarily
To control gigantic hugepage allocation, skip processing hugepage kernel
arguments (default_hugepagesz, hugepagesz and hugepages) when
hugepages_supported() returns false.
Note for backporting: This fix is a partial reversion of the commit
mentioned in the Fixes tag and is only valid once the change referenced by
the Depends-on tag is present. When backporting this patch, the commit
mentioned in the Depends-on tag must be included first.
Link: https://lore.kernel.org/all/20250121150419.1342794-1-sourabhjain@linux.ibm.com/ [1]
Link: https://lore.kernel.org/all/20250128043358.163372-1-sourabhjain@linux.ibm.com/ [2]
Link: https://lkml.kernel.org/r/20251224115524.1272010-1-sourabhjain@linux.ibm.com
Fixes:
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|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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. 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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