Re: [PATCH v4 3/6] KVM: arm64: nv: Add nested revmap broken tracepoint

[Marc Zyngier]

On Thu, 16 Jul 2026 07:45:05 +0100,
Oliver Upton <oupton@xxxxxxxxxx> wrote:
> 
> Hi Wei-Lin,
> 
> On Tue, Jul 14, 2026 at 12:59:22PM +0100, Wei-Lin Chang wrote:
> > Add a tracepoint to track when a nested reverse map becomes broken. This
> > makes it easier to detect NV performance degradation caused by full
> > shadow stage-2 unmaps.
> > 
> > Signed-off-by: Wei-Lin Chang <weilin.chang@xxxxxxx>
> 
> I'm not too excited about making a tracepoint out of this, especially
> since a 'broken' reverse map is more of a KVM implementation detail
> (that could change) than anything else.
> 
> BPF is quite popular at this point, do you think it's reasonable to
> instead expect the curious KVM developer to attach a kprobe and inspect
> the state of the nested MMU?

I was the one asking for a way to report this stuff. I'd be completely
fine with BPF as long as we give the recipe for this so that people
can readily look at this.

Even better, find a way not to have a broken rmap the first place ;-).

Thanks,

	M.

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