Re: [PATCH] KVM: arm64: Stop printing about MMIO accesses where ISV==0

[Marc Zyngier <maz@kernel.org>]

On Wed, 25 Oct 2023 09:25:07 +0100,
Oliver Upton <oliver.upton@linux.dev> wrote:
> 
> On Wed, Oct 25, 2023 at 09:04:58AM +0100, Marc Zyngier wrote:
> 
> [...]
> 
> > While I totally agree that this *debug* statement should go, we should
> > also replace it with something else.
> > 
> > Because when you're trying to debug a guest (or even KVM itself),
> > seeing this message is a sure indication that the guest is performing
> > an access outside of memory. The fact that KVM tries to handle it as
> > MMIO is just an implementation artefact.
> > 
> > So I'd very much welcome a replacement tracepoint giving a bit more
> > information, such as guest PC, IPA being accessed, load or store. With
> > that, everybody wins.
> 
> Aren't we already covered by the kvm_guest_fault tracepoint? Userspace
> can filter events on ESR to get the faults it cares about. I'm not
> against adding another tracepoint, but in my experience kvm_guest_fault
> has been rather useful for debugging any type of guest fault.

That tracepoint is one of the most triggered, and sifting through this
is a painful experience. If we go down that road, adding a bit of
extra documentation (pointed to from the KVM_RUN entry) and an example
filter script would be most useful.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.