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

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Message-ID: <87ed4uveam.wl-maz@kernel.org>
Date: Sat, 05 Oct 2024 15:02:09 +0100
From: Marc Zyngier <maz@...nel.org>
To: Mark Brown <broonie@...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, 05 Oct 2024 14:48:09 +0100,
Mark Brown <broonie@...nel.org> wrote:
> 
> [1  <text/plain; us-ascii (7bit)>]
> 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.

From that very file:

/*
 * Map encoding to trap bits for exception reported with EC=0x18.
 [...]
 */

Everything else needs special handling.

	M.

-- 
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