bbbb65770b
In system_supports_bti() we use cpus_have_const_cap() to check for ARM64_HAS_BTI, but this is not necessary and alternative_has_cap_*() or cpus_have_final_*cap() would be preferable. For historical reasons, cpus_have_const_cap() is more complicated than it needs to be. Before cpucaps are finalized, it will perform a bitmap test of the system_cpucaps bitmap, and once cpucaps are finalized it will use an alternative branch. This used to be necessary to handle some race conditions in the window between cpucap detection and the subsequent patching of alternatives and static branches, where different branches could be out-of-sync with one another (or w.r.t. alternative sequences). Now that we use alternative branches instead of static branches, these are all patched atomically w.r.t. one another, and there are only a handful of cases that need special care in the window between cpucap detection and alternative patching. Due to the above, it would be nice to remove cpus_have_const_cap(), and migrate callers over to alternative_has_cap_*(), cpus_have_final_cap(), or cpus_have_cap() depending on when their requirements. This will remove redundant instructions and improve code generation, and will make it easier to determine how each callsite will behave before, during, and after alternative patching. When CONFIG_ARM64_BTI_KERNEL=y, the ARM64_HAS_BTI cpucap is a strict boot cpu feature which is detected and patched early on the boot cpu. All uses guarded by CONFIG_ARM64_BTI_KERNEL happen after the boot CPU has detected ARM64_HAS_BTI and patched boot alternatives, and hence can safely use alternative_has_cap_*() or cpus_have_final_boot_cap(). Regardless of CONFIG_ARM64_BTI_KERNEL, all other uses of ARM64_HAS_BTI happen after system capabilities have been finalized and alternatives have been patched. Hence these can safely use alternative_has_cap_*) or cpus_have_final_cap(). This patch splits system_supports_bti() into system_supports_bti() and system_supports_bti_kernel(), with the former handling where the cpucap affects userspace functionality, and ther latter handling where the cpucap affects kernel functionality. The use of cpus_have_const_cap() is replaced by cpus_have_final_cap() in cpus_have_const_cap, and cpus_have_final_boot_cap() in system_supports_bti_kernel(). This will avoid generating code to test the system_cpucaps bitmap and should be better for all subsequent calls at runtime. The use of cpus_have_final_cap() and cpus_have_final_boot_cap() will make it easier to spot if code is chaanged such that these run before the ARM64_HAS_BTI cpucap is guaranteed to have been finalized. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Reviewed-by: Mark Brown <broonie@kernel.org> Cc: Ard Biesheuvel <ardb@kernel.org> Cc: Suzuki K Poulose <suzuki.poulose@arm.com> Cc: Will Deacon <will@kernel.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> |
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| Documentation | ||
| LICENSES | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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.
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.