Messages in this thread | | | Date | Tue, 08 Aug 2023 12:06:45 +0100 | From | Marc Zyngier <> | Subject | Re: [RFC PATCH 0/3] coresight: Support exclude_guest with Feat_TRF and nVHE |
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On Sat, 05 Aug 2023 11:28:39 +0100, Suzuki K Poulose <suzuki.poulose@arm.com> wrote: > > 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.
I just quickly reviewed the first two patches of the nVHE series, and I think the shape is a bit wrong. I can absolutely see the interest of preventing extra tracing when a guest is running, but the way this is currently plugged makes it hard to reason about it.
> [0] https://lkml.kernel.org/r/20230804085219.260790-1-james.clark@arm.com
I'll try to have a look at that one later.
Thanks,
M.
-- Without deviation from the norm, progress is not possible.
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