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

From: Marc Zyngier <maz@kernel.org>
To: Mark Brown <broonie@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Oliver Upton <oliver.upton@linux.dev>,
	James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Fuad Tabba <tabba@google.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev
Subject: Re: [PATCH 2/4] arm64/fpsimd: Discover maximum vector length implemented by any CPU
Date: Wed, 05 Jun 2024 13:13:20 +0100	[thread overview]
Message-ID: <86bk4flh9b.wl-maz@kernel.org> (raw)
In-Reply-To: <20240605-kvm-arm64-fix-pkvm-sve-vl-v1-2-680d6b43b4c1@kernel.org>

On Wed, 05 Jun 2024 12:41:28 +0100,
Mark Brown <broonie@kernel.org> wrote:
> 
> @@ -1083,6 +1095,18 @@ int vec_verify_vq_map(enum vec_type type)
>  	if (!IS_ENABLED(CONFIG_KVM) || !is_hyp_mode_available())
>  		return 0;
>  
> +	/*
> +	 * 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()).

	M.

-- 
Without deviation from the norm, progress is not possible.