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

[Marc Zyngier <maz@kernel.org>]

On Mon, 06 Jan 2025 14:24:35 +0000,
James Clark <james.clark@linaro.org> 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.

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