linux-kernel - Re: [PATCH v5 05/19] arm64: Add support for trace synchronization barrier

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Message-ID: <87tup0ikf0.wl-maz@kernel.org>
Date:   Wed, 24 Mar 2021 16:30:27 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        coresight@...ts.linaro.org, mike.leach@...aro.org,
        leo.yan@...aro.org, anshuman.khandual@....com,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH v5 05/19] arm64: Add support for trace synchronization barrier

On Wed, 24 Mar 2021 16:25:12 +0000,
Suzuki K Poulose <suzuki.poulose@....com> wrote:
> 
> On 24/03/2021 16:16, Marc Zyngier wrote:
> > On Wed, 24 Mar 2021 15:51:14 +0000,
> > Suzuki K Poulose <suzuki.poulose@....com> wrote:
> >> 
> >> On 24/03/2021 13:49, Marc Zyngier wrote:
> >>> On Wed, 24 Mar 2021 09:39:13 +0000,
> >>> Suzuki K Poulose <suzuki.poulose@....com> wrote:
> >>>> 
> >>>> On 23/03/2021 18:21, Catalin Marinas wrote:
> >>>>> Hi Suzuki?
> >>>>> 
> >>>>> On Tue, Mar 23, 2021 at 12:06:33PM +0000, Suzuki K Poulose wrote:
> >>>>>> tsb csync synchronizes the trace operation of instructions.
> >>>>>> The instruction is a nop when FEAT_TRF is not implemented.
> >>>>>> 
> >>>>>> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> >>>>>> Cc: Mike Leach <mike.leach@...aro.org>
> >>>>>> Cc: Catalin Marinas <catalin.marinas@....com>
> >>>>>> Cc: Will Deacon <will.deacon@....com>
> >>>>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> >>>>> 
> >>>>> How do you plan to merge these patches? If they go via the coresight
> >>>>> tree:
> >>>>> 
> >>>> 
> >>>> Ideally all of this should go via the CoreSight tree to have the
> >>>> dependencies solved at one place. But there are some issues :
> >>>> 
> >>>> If this makes to 5.13 queue for CoreSight,
> >>>> 
> >>>> 1) CoreSight next is based on rc2 at the moment and we have fixes gone
> >>>> into rc3 and later, which this series will depend on. (We could move
> >>>> the next tree forward to a later rc to solve this).
> >>>> 
> >>>> 2) There could be conflicts with the kvmarm tree for the KVM host
> >>>> changes (That has dependency on the TRBE definitions patch).
> >>>> 
> >>>> If it doesn't make to 5.13 queue, it would be good to have this patch,
> >>>> the TRBE defintions and the KVM host patches queued for 5.13 (not sure
> >>>> if this is acceptable) and we could rebase the CoreSight changes on 5.13
> >>>> and push it to next release.
> >>>> 
> >>>> I am open for other suggestions.
> >>>> 
> >>>> Marc, Mathieu,
> >>>> 
> >>>> Thoughts ?
> >>> 
> >>> I was planning to take the first two patches in 5.12 as fixes (they
> >>> are queued already, and would hopefully land in -rc5). If that doesn't
> >>> fit with the plan, please let me know ASAP.
> >> 
> >> Marc,
> >> 
> >> I think it would be better to hold on pushing those patches until we
> >> have a clarity on how things will go.
> > 
> > OK. I thought there was a need for these patches to prevent guest
> > access to the v8.4 self hosted tracing feature that went in 5.12
> > though[1]... Did I get it wrong?
> 
> Yes, that is correct. The guest could access the Trace Filter Control
> register and fiddle with the host settings, without this patch.
> e.g, it could disable tracing at EL0/EL1, without the host being
> aware on nVHE host.

OK, so we definitely do need these patches, don't we? Both? Just one?
Please have a look at kvmarm/fixes and tell me what I must keep.

Thanks,

	M.

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