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When returning to a user context, the arm64 entry code masks all DAIF exceptions before handling pending work in exit_to_user_mode_prepare() and do_notify_resume(), where it will transiently unmask all DAIF exceptions. This is a holdover from the old entry assembly, which conservatively masked all DAIF exceptions, and it's only necessary to mask interrupts at this point during the exception return path, so long as we subsequently mask all DAIF exceptions before the actual exception return. While most DAIF manipulation follows a save...restore sequence, the manipulation in do_notify_resume() is the other way around, unmasking all DAIF exceptions before masking them again. This is unfortunate as we unnecessarily mask Debug and SError exceptions, and it would be nice to remove this special case to make DAIF manipulation simpler and most consistent. This patch changes exit_to_user_mode_prepare() and do_notify_resume() to only mask interrupts while handling pending work, masking other DAIF exceptions after this has completed. This removes the unusual DAIF manipulation and allows Debug and SError exceptions to be taken for a slightly longer window during the exception return path. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: James Morse <james.morse@arm.com> Cc: Mark Brown <broonie@kernel.org> Cc: Will Deacon <will@kernel.org> Reviewed-by: Mark Brown <broonie@kernel.org> Link: https://lore.kernel.org/r/20240206123848.1696480-4-mark.rutland@arm.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Tested-by: Itaru Kitayama <itaru.kitayama@linux.dev> |
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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.