linux-kernel - Re: [PATCH v13 16/40] KVM: arm64: Manage GCS access and registers for guests

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Message-ID: <86a5fm7b4i.wl-maz@kernel.org>
Date: Wed, 02 Oct 2024 16:55:25 +0100
From: Marc Zyngier <maz@...nel.org>
To: Mark Brown <broonie@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Jonathan Corbet <corbet@....net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	James Morse <james.morse@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Arnd Bergmann <arnd@...db.de>,
	Oleg Nesterov <oleg@...hat.com>,
	Eric Biederman <ebiederm@...ssion.com>,
	Shuah Khan <shuah@...nel.org>,
	"Rick P. Edgecombe" <rick.p.edgecombe@...el.com>,
	Deepak Gupta <debug@...osinc.com>,
	Ard Biesheuvel <ardb@...nel.org>,
	Szabolcs Nagy <Szabolcs.Nagy@....com>,
	Kees Cook <kees@...nel.org>,
	"H.J. Lu" <hjl.tools@...il.com>,
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	Christian Brauner <brauner@...nel.org>,
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	Wilco Dijkstra <wilco.dijkstra@....com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-doc@...r.kernel.org,
	kvmarm@...ts.linux.dev,
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Subject: Re: [PATCH v13 16/40] KVM: arm64: Manage GCS access and registers for guests

On Wed, 02 Oct 2024 01:24:25 +0100,
Marc Zyngier <maz@...nel.org> wrote:
> 
> On Tue, 01 Oct 2024 23:58:55 +0100,
> Mark Brown <broonie@...nel.org> wrote:
> 
> > @@ -4714,6 +4735,10 @@ void kvm_calculate_traps(struct kvm_vcpu *vcpu)
> >  		kvm->arch.fgu[HFGxTR_GROUP] |= (HFGxTR_EL2_nPOR_EL1 |
> >  						HFGxTR_EL2_nPOR_EL0);
> >  
> > +	if (!kvm_has_gcs(kvm))
> > +		kvm->arch.fgu[HFGxTR_GROUP] |= (HFGxTR_EL2_nGCS_EL0 |
> > +						HFGxTR_EL2_nGCS_EL1);
> > +
> 
> Why are you still allowing the GCS instructions when GCS isn't
> enabled?

Scratch that, they are NOPs when GCS isn't enabled, so there shouldn't
be any need for extra traps.

	M.

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