linux-kernel - Re: [PATCH v3 03/23] arm64: Make cpu_logical

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Date:   Wed, 2 Dec 2020 15:44:35 +0000
From:   David Brazdil <dbrazdil@...gle.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     kvmarm@...ts.cs.columbia.edu, Jonathan Corbet <corbet@....net>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Sudeep Holla <sudeep.holla@....com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kernel-team@...roid.com
Subject: Re: [PATCH v3 03/23] arm64: Make cpu_logical_map() take unsigned int

On Thu, Nov 26, 2020 at 05:28:38PM +0000, Mark Rutland wrote:
> On Thu, Nov 26, 2020 at 03:54:01PM +0000, David Brazdil wrote:
> > CPU index should never be negative. Change the signature of
> > (set_)cpu_logical_map to take an unsigned int.
> > 
> > Signed-off-by: David Brazdil <dbrazdil@...gle.com>
> 
> Is there a function problem here, or is this just cleanup from
> inspection?
> 
> Core code including the cpuhp_*() callbacks uses an int, so if there's a
> strong justification to change this, it suggests there's some treewide
> cleanup that should be done.
> 
> I don't have strong feelings on the matter, but I'd like to understand
> the rationale.

Yeah, it's a mess. Marc and I felt that using a uint was less error-prone wrt
bounds checks. If this gets an int, it still works and only checking the upper
bound is required. Does that make sense?

David