linux-kernel - Re: [PATCH 1/7] 2 1-byte checks more safer for memory_is_poisoned

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Message-ID: <20180318132126.GA565@n2100.armlinux.org.uk>
Date:   Sun, 18 Mar 2018 13:21:27 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Abbott Liu <liuwenliang@...wei.com>
Cc:     aryabinin@...tuozzo.com, marc.zyngier@....com,
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Subject: Re: [PATCH 1/7] 2 1-byte checks more safer for memory_is_poisoned_16

On Sun, Mar 18, 2018 at 08:53:36PM +0800, Abbott Liu wrote:
> Because in some architecture(eg. arm) instruction set, non-aligned
> access support is not very well, so 2 1-byte checks is more
> safer than 1 2-byte check. The impact on performance is small
> because 16-byte accesses are not too common.

This is unnecessary:

1. a load of a 16-bit quantity will work as desired on modern ARMs.
2. Networking already relies on unaligned loads to work as per x86
   (iow, an unaligned 32-bit load loads the 32-bits at the address
   even if it's not naturally aligned, and that also goes for 16-bit
   accesses.)

If these are rare (which you say above - "not too common") then it's
much better to leave the code as-is, because it will most likely be
faster on modern CPUs, and the impact for older generation CPUs is
likely to be low.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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