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After the recently introduced support for level-triggered mapped interrupt, I accidentally left the VCPU thread busily going back and forward between the guest and the hypervisor whenever the guest was blocking, because I would always incorrectly report that a timer interrupt was pending. This is because the timer->irq.level field is not valid for mapped interrupts, where we offload the level state to the hardware, and as a result this field is always true. Luckily the problem can be relatively easily solved by not checking the cached signal state of either timer in kvm_timer_should_fire() but instead compute the timer state on the fly, which we do already if the cached signal state wasn't high. In fact, the only reason for checking the cached signal state was a tiny optimization which would only be potentially faster when the polling loop detects a pending timer interrupt, which is quite unlikely. Instead of duplicating the logic from kvm_arch_timer_handler(), we enlighten kvm_timer_should_fire() to report something valid when the timer state is loaded onto the hardware. We can then call this from kvm_arch_timer_handler() as well and avoid the call to __timer_snapshot_state() in kvm_arch_timer_get_input_level(). Reported-by: Tomasz Nowicki <tn@semihalf.com> Tested-by: Tomasz Nowicki <tn@semihalf.com> Reviewed-by: Marc Zyngier <marc.zyngier@arm.com> Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org> |
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| README | ||
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. 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.