Hi Marc

On 04/08/2023 20:09, Marc Zyngier wrote:

On Fri, 04 Aug 2023 11:13:10 +0100, James Clark james.clark@arm.com wrote:

...

Hi,

I'm looking for help in testing this and for feedback on whether it's useful to anyone. Testing it requires hardware that has Feat_TRF (v8.4) but no TRBE. This is because TRBE usage is disabled in nVHE guests.

I don't currently have any access to any hardware, and the FVP model can only do self hosted trace using TRBE.

Currently with nVHE you would always get trace from guests, and filtering out isn't possible without this patchset. In comparison, with VHE guests, they never generate guest trace without [1]. I think the existence of trace rather than lack of could suggest that this change is less useful than [1]. Also the restricted set of hardware that it works on supports that too.

It'd be nice to have some sort of feature parity, but it seems like a vanishingly small target of users having access to an ETM sink.

...

Apart from compilation and checking that the exclude guest settings are correctly programmed on guest switch, this is untested by me.

I'll have a look at the series, but none of my HW fits in this description (my ARMv8.4+ boxes don't have any form of tracing).

While I have your attention, we have another series that manages the trace filtering for Guests on VHE, completely within the Coresight etm4x driver here [0]. I personally think, it is good to have the guest filtering for both nVHE and VHE under the KVM control, like we do in this series. I would like your opinion on this.

[0] https://lkml.kernel.org/r/20230804085219.260790-1-james.clark@arm.com

Suzuki

Thanks,

M.