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1b558e14f3
apic_pending_intr_clear() is fundamentally voodoo programming. It's primary
purpose is to clear stale ISR bits in the local APIC, which would otherwise
lock the corresponding interrupt priority level.
The comments and the implementation claim falsely that after clearing the
stale ISR bits, eventually stale IRR bits would be turned into ISR bits and
can be cleared as well. That's just wishful thinking because:
1) If interrupts are disabled, the APIC does not propagate an IRR bit to
the ISR.
2) If interrupts are enabled, then the APIC propagates the IRR bit to the
ISR and raises the interrupt in the CPU, which means that code _cannot_
observe the ISR bit for any of those IRR bits.
Rename the function to reflect the purpose and make exactly _one_ attempt
to EOI the pending ISR bits and add comments why traversing the pending bit
map in low to high priority order is correct.
Instead of trying to "clear" IRR bits, simply print a warning message when
the IRR is not empty.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/871ppwih4s.ffs@tglx
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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 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.