Date: Thu, 8 Feb 2024 12:13:54 +0000
From: Catalin Marinas <catalin.marinas@arm.com>
To: Marc Zyngier <maz@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
	Will Deacon <will@kernel.org>, Mark Rutland <mark.rutland@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Ard Biesheuvel <ardb@kernel.org>, James Morse <james.morse@arm.com>,
	Oliver Upton <oliver.upton@linux.dev>,
	Zenghui Yu <yuzenghui@huawei.com>
Subject: Re: [PATCH v4 02/10] arm64: cpufeatures: Correctly handle signed
 values
Message-ID: <ZcTFgpm8HlmP2XUK@arm.com>
References: <20240122181344.258974-1-maz@kernel.org>
 <20240122181344.258974-3-maz@kernel.org>
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In-Reply-To: <20240122181344.258974-3-maz@kernel.org>

On Mon, Jan 22, 2024 at 06:13:36PM +0000, Marc Zyngier wrote:
> Although we've had signed values for some features such as PMUv3
> and FP, the code that handles the comparaison with some limit
> has a couple of annoying issues:
> 
> - the min_field_value is always unsigned, meaning that we cannot
>   easily compare it with a negative value
> 
> - it is not possible to have a range of values, let alone a range
>   of negative values
> 
> Fix this by:
> 
> - adding an upper limit to the comparison, defaulting to all bits
>   being set to the maximum positive value
> 
> - ensuring that the signess of the min and max values are taken into
>   account
> 
> A ARM64_CPUID_FIELDS_NEG() macro is provided for signed features, but
> nothing is using it yet.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>