linux-kernel - Re: [PATCH] KVM: arm64: Only default to enabling SVE when present

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Message-ID: <d090e3db-ebed-4cc8-a1f8-a2c15f8a39b1@sirena.org.uk>
Date:   Thu, 14 Sep 2023 11:32:12 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Oliver Upton <oliver.upton@...ux.dev>
Cc:     Marc Zyngier <maz@...nel.org>, James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: arm64: Only default to enabling SVE when present

On Thu, Sep 14, 2023 at 12:04:29AM +0000, Oliver Upton wrote:
> On Wed, Sep 13, 2023 at 07:34:16PM +0100, Mark Brown wrote:

> > -		if (!vcpu_has_sve(vcpu) ||
> > -		    (vcpu->arch.fp_state != FP_STATE_GUEST_OWNED))
> > +		if (cpus_have_final_cap(ARM64_SVE) &&
> > +		    (!vcpu_has_sve(vcpu) ||
> > +		     (vcpu->arch.fp_state != FP_STATE_GUEST_OWNED)))

> vcpu_has_sve() already tests system_supports_sve(), so I don't believe
> this hunk is necessary.

That'll mean that the first branch of the || should always return true
on systems without SVE so we'll set CPTR_EL2_TZ, and there's also the
check for guest ownership as well.

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