[RFC PATCH 00/45] KVM: arm/arm64: Rework virtual GIC emulation

André Przywara andre.przywara at arm.com
Wed Apr 13 09:07:56 PDT 2016

On 31/03/16 19:30, Christoffer Dall wrote:
> On Fri, Mar 25, 2016 at 02:04:23AM +0000, Andre Przywara wrote:
>> This series is a joint effort to re-implement KVM's GIC emulation.
>> While the current implementation is centered around providing
>> efficient MMIO emulation, the hot path for most guests is actually
>> the guest entry and exit, which currently is rather costly.
>> Also the existing emulation has a global distributor lock, which
>> quickly becomes a bottleneck once the number of VCPUs increases.
>> Additionally the emulation was originally designed for GICv2, adding
>> GICv3 ITS emulation support to this proved to be rather painful.
>> Last, but not least the existing code became less and less
>> maintainable, with many special cases handled explicitly.
>> The new implementation is build around a struct vgic_irq data data
>> structure, which holds all information about a virtual interrupt.
>> Interruts which should be injected are hold in a per-VCPU list, this
>> make the entry/exit path much more efficient. Also the new structure
>> allows to have more fine grained locking - per IRQ and per VCPU -
>> getting rid of the global distributor lock.
>> As a result of the new design ITS emulation fits in more nicely, the
>> respective code will be provided as a follow-up series.
>> This series implements the same feature set as the existing emulation,
>> as a goodie we now implement priorities correctly.
>> To allow an easy transition with good test coverage, but still maintain
>> stability, both implementations live side by side, selectable via a
>> Kconfig option. The default is the new implementation.
>> If this code proves to be reliable, we will later remove the current
>> implementation with an extra patch set.
>> Please have a look at the series, review it and give the code some
>> serious testing (and possibly debugging). All feedback is appreciated.
> Hmph, starting a guest a couple of times and running hackbench inside
> the guest actually gave me (twice) the following error:
> NMI watchdog: BUG: soft lockup - CPU#0 stuck for 23s! [kworker/0:0:4]

On the host or in the guest?
Can you reproduce it easily? If yes, can you add some lock debugging to
see if we are stuck in a spinlock?


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