Re: [PATCH] KVM: arm64: Disable TRBE Trace Buffer Unit when running in guest context

Will Deacon
2026-02-17T12:26:06Z

On Tue, Feb 17, 2026 at 12:20:14PM +0000, James Clark wrote:
> On 16/02/2026 5:32 pm, Will Deacon wrote:
> > On Mon, Feb 16, 2026 at 02:29:31PM +0000, Marc Zyngier wrote:
> > > And even then, I'm tempted to simply get rid of any sort of
> > > guest-only tracing, given that TRBE is not capable of representing
> > > exceptions that are synthesised by the host, making it the resulting
> > > traces useless.
> >
> > I think that effectively means reverting the series merged from here:
> >
> > https://lore.kernel.org/all/20250106142446.628923-1-james.clark@linaro.org/
> >
> > but then we still need to clear TRBLIMITR_EL1.E.
> >
>
> Removing that series would actually have the effect of turning guest trace
> on in nVHE for non-TRBE sinks. The reason for implementing the filtering was
> to turn guest trace off because a user didn't want to see it.

What I meant was, revert that series and then also ensure that both TRFCR
and TRBLIMITR are always zero while running in the guest. Is that not
sufficient?

Will