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

[James Clark <james.clark@linaro.org>]

On 06/01/2025 2:48 pm, Marc Zyngier wrote:
> 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.
> 

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

Thanks
James