linux-kernel - Re: [PATCH v14 3/5] KVM: arm64: Manage GCS access and registers for guests

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Message-ID: <ZwFDmaeIgPKfmJnj@finisterre.sirena.org.uk>
Date: Sat, 5 Oct 2024 14:48:09 +0100
From: Mark Brown <broonie@...nel.org>
To: Marc Zyngier <maz@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Shuah Khan <shuah@...nel.org>, linux-arm-kernel@...ts.infradead.org,
	linux-doc@...r.kernel.org, kvmarm@...ts.linux.dev,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v14 3/5] KVM: arm64: Manage GCS access and registers for
 guests

On Sat, Oct 05, 2024 at 02:18:57PM +0100, Marc Zyngier wrote:
> Mark Brown <broonie@...nel.org> wrote:
> > On Sat, Oct 05, 2024 at 12:34:20PM +0100, Marc Zyngier wrote:

> > > Where is the handling of traps resulting of HFGITR_EL2.nGCSSTR_EL1?

> > These will trap with an EC of 0x2d which isn't known so I was expecting
> > this to get handled in the same way as for example a return of false
> > from kvm_hyp_handle_fpsimd() for SVE when unsupported, or for the
> > simiarly unknown SME EC, currently.  I gather from your comment that
> > you're instead expecting to see an explicit exit handler for this EC
> > that just injects the UNDEF directly?

> Not just inject an UNDEF directly, but also track whether this needs
> to be forwarded when the guest's HFGITR_EL2.nGCSSTR_EL1 is 0 while not
> being not RES0. Basically following what the pseudocode describes.

Ah, I see.  I'd been under the impression that the generic machinery was
supposed to handle this already using the descriptions in
emulate-nested.c and we only needed handlers for more specific actions.

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