mainlining shenanigans
df3fb96820
Currently the FPSIMD handling code uses the condition task->mm == NULL as a hint that task has no FPSIMD register context. The ->mm check is only there to filter out tasks that cannot possibly have FPSIMD context loaded, for optimisation purposes. Also, TIF_FOREIGN_FPSTATE must always be checked anyway before saving FPSIMD context back to memory. For these reasons, the ->mm checks are not useful, providing that TIF_FOREIGN_FPSTATE is maintained in a consistent way for all threads. The context switch logic is already deliberately optimised to defer reloads of the regs until ret_to_user (or sigreturn as a special case), and save them only if they have been previously loaded. These paths are the only places where the wrong_task and wrong_cpu conditions can be made false, by calling fpsimd_bind_task_to_cpu(). Kernel threads by definition never reach these paths. As a result, the wrong_task and wrong_cpu tests in fpsimd_thread_switch() will always yield true for kernel threads. This patch removes the redundant checks and special-case code, ensuring that TIF_FOREIGN_FPSTATE is set whenever a kernel thread is scheduled in, and ensures that this flag is set for the init task. The fpsimd_flush_task_state() call already present in copy_thread() ensures the same for any new task. With TIF_FOREIGN_FPSTATE always set for kernel threads, this patch ensures that no extra context save work is added for kernel threads, and eliminates the redundant context saving that may currently occur for kernel threads that have acquired an mm via use_mm(). Signed-off-by: Dave Martin <Dave.Martin@arm.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Christoffer Dall <christoffer.dall@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> |
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| firmware | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.