Re: [PATCH v9 0/7] kvm/coresight: Support exclude guest and exclude host

[James Clark]

On 06/01/2025 2:48 pm, Marc Zyngier wrote:
> On Mon, 06 Jan 2025 14:24:35 +0000,
> James Clark <james.clark@xxxxxxxxxx> wrote:
> > FEAT_TRF is a Coresight feature that allows trace capture to be
> > completely filtered at different exception levels, unlike the existing
> > TRCVICTLR controls which may still emit target addresses of branches,
> > even if the following trace is filtered.
> >
> > Without FEAT_TRF, it was possible to start a trace session on a host and
> > also collect trace from the guest as TRCVICTLR was never programmed to
> > exclude guests (and it could still emit target addresses even if it
> > was).
> >
> > With FEAT_TRF, the current behavior of trace in guests exists depends on
> > whether nVHE or VHE are being used. Both of the examples below are from
> > the host's point of view, as Coresight isn't accessible from guests.
> > This patchset is only relevant to when FEAT_TRF exists, otherwise there
> > is no change.
> >
> > Current behavior:
> >
> >    nVHE/pKVM:
> >
> >    Because the host and the guest are both using TRFCR_EL1, trace will be
> >    generated in guests depending on the same filter rules the host is
> >    using. For example if the host is tracing userspace only, then guest
> >    userspace trace will also be collected.
> >
> >    (This is further limited by whether TRBE is used because an issue
> >    with TRBE means that it's completely disabled in nVHE guests, but it's
> >    possible to have other tracing components.)
> >
> >    VHE:
> >
> >    With VHE, the host filters will be in TRFCR_EL2, but the filters in
> >    TRFCR_EL1 will be active when the guest is running. Because we don't
> >    write to TRFCR_EL1, guest trace will be completely disabled.
> >
> > New behavior:
> >
> > The guest filtering rules from the Perf session are now honored for both
> > nVHE and VHE modes. This is done by either writing to TRFCR_EL12 at the
> > start of the Perf session and doing nothing else further, or caching the
> > guest value and writing it at guest switch for nVHE. In pKVM, trace is
> > now be disabled for both protected and unprotected guests.
> >
> > There is also an optimization where the Coresight drivers pass their
> > enabled state to KVM. This means in the common case KVM doesn't have to
> > touch any sysregs when the feature isn't in use.
> >
> > Applies to kvmarm/next (00163be8bb59).
>
> Can you *PLEASE* stop this absolutely nonsense of posting patches
> based on top of random commits? Please look at how we integrate new
> developments: they are *always* based on an early -rc tag (usually
> -rc3).
>
> If you depend on other patches, add them to your series and post the
> whole thing.
>
> Thanks,
>
> 	M.

Sure, I re-posted it on the latest -rc with a few commits picked up.

Thanks
James