linux-kernel - Re: [PATCH 2/4] arm64/fpsimd: Discover maximum vector length implemented by any CPU

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Message-ID: <1875ba4e-02c7-4331-b9c6-7ab68d2157b3@sirena.org.uk>
Date: Wed, 5 Jun 2024 13:31:38 +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>,
	James Morse <james.morse@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Fuad Tabba <tabba@...gle.com>, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, kvmarm@...ts.linux.dev
Subject: Re: [PATCH 2/4] arm64/fpsimd: Discover maximum vector length
 implemented by any CPU

On Wed, Jun 05, 2024 at 01:13:20PM +0100, Marc Zyngier wrote:
> Mark Brown <broonie@...nel.org> wrote:

> > +	/*
> > +	 * pKVM allocates and uses storage for host state based on the
> > +	 * largest per-PE VL, reject new PEs with a larger maximum.
> > +	 */
> > +	if (is_protected_kvm_enabled()) {
> > +		if (max_vl > info->max_cpu_vl) {
> > +			pr_warn("%s: cpu%d: would increase maximum VL\n",
> > +				info->name, smp_processor_id());
> > +			return -EINVAL;
> > +		}
> > +	}

> Once protected mode is enabled, no new CPU can be booted (see
> psci_relay.c::psci_cpu_on()).

Ah, that's a bit easier.  Might still be worth keeping the check just in
case that changes or we acquire some further use of this value but it's
not currently needed and the comment could be updated.

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