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

Christoffer Dall
2016-03-31T18:29:15Z

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]

(that is using your branch on Mustang).

-Christoffer