REGRESSION: Upgrading host kernel from 5.11 to 5.13 breaks QEMU guests - perf/fw_devlink/kvm

[Andrew Jones]

On Mon, Sep 20, 2021 at 10:45:26AM +0100, Russell King (Oracle) wrote:
> On Sun, Sep 19, 2021 at 02:36:46PM +0100, Marc Zyngier wrote:
> > Urgh. That's a bummer. T1he PMU driver only comes up once it has found
> > its interrupt controller, which on the Armada 8040 is not the GIC, but
> > some weird thing on the side that doesn't actually serve any real
> > purpose. On HW where the PMU is directly wired into the GIC, it all
> > works fine, though by luck rather than by design.
> > 
> > Anyway, rant over. This is a bug that needs addressing so that KVM can
> > initialise correctly irrespective of the probing order. This probably
> > means that the static key controlling KVM's behaviour wrt the PMU must
> > be controlled by the PMU infrastructure itself, rather than KVM trying
> > to probe for it.
> > 
> > Can you please give the following hack a go (on top of 5.15-rc1)? I've
> > briefly tested it on my McBin, and it did the trick. I've also tested
> > it on the M1 (which really doesn't have an architectural PMU) to
> > verify that it was correctly failing.
> 
> My test program that derives the number of registers qemu uses now
> reports 236 registers again and I see:

Hi Russell,

You may be interested in kvm selftests and this one[1] in particular.

[1] tools/testing/selftests/kvm/aarch64/get-reg-list.c

Thanks,
drew


> 
> kvm [7]: PMU detected and enabled
> 
> in the kernel boot log.
> 
> Tested-by: Russell King (Oracle) <rmk+kernel at armlinux.org.uk>
> 
> Thanks.
> 
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