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When fully emulating a timer, we back it with a hrtimer that is
armver on vcpu_load(). However, we do this even if the timer is
already pending.
This causes spurious interrupts to be taken, though the guest
doesn't observe them (the interrupt is already pending).
Although this is a waste of precious cycles, this isn't the
end of the world with the current state of KVM. However, this
can lead to a situation where a guest doesn't make forward
progress anymore with NV.
Fix it by checking that if the timer is already pending
before arming a new hrtimer. Also drop the hrtimer cancelling,
which is useless, by construction.
Reported-by: D Scott Phillips <scott@os.amperecomputing.com>
Fixes: bee038a674 ("KVM: arm/arm64: Rework the timer code to use a timer_map")
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230112123829.458912-2-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
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.