mirror of
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-03-22 07:27:12 +08:00
a5baf582f4
The only remaining reason why EFI runtime services are invoked with preemption disabled is the fact that the mm is swapped out behind the back of the context switching code. The kernel no longer disables preemption in kernel_neon_begin(). Furthermore, the EFI spec is being clarified to explicitly state that only baseline FP/SIMD is permitted in EFI runtime service implementations, and so the existing kernel mode NEON context switching code is sufficient to preserve and restore the execution context of an in-progress EFI runtime service call. Most EFI calls are made from the efi_rts_wq, which is serviced by a kthread. As kthreads never return to user space, they usually don't have an mm, and so we can use the existing infrastructure to swap in the efi_mm while the EFI call is in progress. This is visible to the scheduler, which will therefore reactivate the selected mm when switching out the kthread and back in again. Given that the EFI spec explicitly permits runtime services to be called with interrupts enabled, firmware code is already required to tolerate interruptions. So rather than disable preemption, disable only migration so that EFI runtime services are less likely to cause scheduling delays. To avoid potential issues where runtime services are interrupted while polling the secure firmware for async completions, keep migration disabled so that a runtime service invocation does not resume on a different CPU from the one it was started on. Note, though, that the firmware executes at the same privilege level as the kernel, and is therefore able to disable interrupts altogether. Acked-by: Will Deacon <will@kernel.org> Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Acked-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
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 reStructuredText 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.