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kvm_timer_update_state() is called when changing the phys timer configuration registers, either via vcpu reset, as a result of a trap from the guest, or when userspace programs the registers. phys_timer_emulate() is in turn called by kvm_timer_update_state() to either cancel an existing software timer, or program a new software timer, to emulate the behavior of a real phys timer, based on the change in configuration registers. Unfortunately, the interaction between these two functions left a small race; if the conceptual emulated phys timer should actually fire, but the soft timer hasn't executed its callback yet, we cancel the timer in phys_timer_emulate without injecting an irq. This only happens if the check in kvm_timer_update_state is called before the timer should fire, which is relatively unlikely, but possible. The solution is to update the state of the phys timer after calling phys_timer_emulate, which will pick up the pending timer state and update the interrupt value. Note that this leaves the opportunity of raising the interrupt twice, once in the just-programmed soft timer, and once in kvm_timer_update_state. Since this always happens synchronously with the VCPU execution, there is no harm in this, and the guest ever only sees a single timer interrupt. Cc: Stable <stable@vger.kernel.org> # 4.15+ Signed-off-by: Christoffer Dall <christoffer.dall@arm.com> Signed-off-by: Marc Zyngier <marc.zyngier@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 Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
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.