linux-kernel - Re: [PATCH V3 6/7] arm64/boot: Enable EL2 requirements for FEAT

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Message-ID: <bdd53fdb-9ba2-4d55-870f-9cb40e1e6b21@sirena.org.uk>
Date: Wed, 18 Dec 2024 13:15:58 +0000
From: Mark Brown <broonie@...nel.org>
To: Marc Zyngier <maz@...nel.org>
Cc: Rob Herring <robh@...nel.org>,
	Anshuman Khandual <anshuman.khandual@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Jonathan Corbet <corbet@....net>,
	Oliver Upton <oliver.upton@...ux.dev>,
	James Morse <james.morse@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>,
	kvmarm@...ts.linux.dev, linux-doc@...r.kernel.org
Subject: Re: [PATCH V3 6/7] arm64/boot: Enable EL2 requirements for
 FEAT_Debugv8p9

On Wed, Dec 18, 2024 at 09:10:51AM +0000, Marc Zyngier wrote:

> But I don't think we should be prescriptive about the state of these
> registers, as long as the potential traps are correctly handled.

The rest of the document is written in terms of explicit register
values, if we're changing approach we should probably update all the
existing requirements to be written in the same way since having a mix
of approaches tends to be a big red flag that there should be different
handling.  Consistency will make the document clearer and easier for
people to work with.

FWIW there is an explict note in the document about the fact that it's
an as-if rule:

|                                                Where the values documented
| disable traps it is permissible for these traps to be enabled so long as
| those traps are handled transparently by higher exception levels as though
| the values documented were set.

from when I raised this before.

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