linux-kernel - Re: [PATCH] doc/arm: take care restore order of GICR

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Message-ID: <87czrc2dsu.wl-maz@kernel.org>
Date:   Wed, 21 Jul 2021 10:53:37 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Jianyong Wu <jianyong.wu@....com>
Cc:     james.morse@....com, andre.przywara@....com, lushenming@...wei.com,
        kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        justin.he@....com
Subject: Re: [PATCH] doc/arm: take care restore order of GICR_* in ITS restore

On Wed, 21 Jul 2021 10:20:19 +0100,
Jianyong Wu <jianyong.wu@....com> wrote:
> 
> When restore GIC/ITS, GICR_CTLR must be restored after GICR_PROPBASER
> and GICR_PENDBASER. That is important, as both of GICR_PROPBASER and
> GICR_PENDBASER will fail to be loaded when lpi has enabled yet in
> GICR_CTLR. Keep the restore order above will avoid that issue.
> Shout it out at the doc is very helpful that may avoid lots of debug work.

But that's something that is already mandated by the architecture,
isn't it? See "5.1 LPIs" in the architecture spec:

<quote>

If GICR_PROPBASER is updated when GICR_CTLR.EnableLPIs == 1, the
effects are UNPREDICTABLE.

[...]

If GICR_PENDBASER is updated when GICR_CTLR.EnableLPIs == 1, the
effects are UNPREDICTABLE.

</quote>

The point of this documentation is to make it explicit what is *not*
covered by the architecture. Anything that is in the architecture
still applies, and shouldn't be overlooked.

Thanks,

	M.

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