linux-kernel - Re: [PATCH] mm: alloc_tag: change the KASAN_TAG_WIDTH for HW

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Message-Id: <20250428105716.151167-1-trintaeoitogc@gmail.com>
Date: Mon, 28 Apr 2025 07:57:16 -0300
From: Guilherme Giacomo Simoes <trintaeoitogc@...il.com>
To: akpm@...ux-foundation.org
Cc: andreyknvl@...il.com,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	pasha.tatashin@...een.com,
	surenb@...gle.com,
	trintaeoitogc@...il.com
Subject: Re: [PATCH] mm: alloc_tag: change the KASAN_TAG_WIDTH for HW_TAGS

Andrew Morton <akpm@...ux-foundation.org> wrote: 
> > the KASAN_TAG_WIDTH is 8 bits for both (HW_TAGS and SW_TAGS), but for
> > HW_TAGS the KASAN_TAG_WIDTH can be 4 bits bits because due to the design
> > of the MTE the memory words for storing metadata only need 4 bits.
> > Change the preprocessor define KASAN_TAG_WIDTH for check if SW_TAGS is
> > define, so KASAN_TAG_WIDTH should be 8 bits, but if HW_TAGS is define,
> > so KASAN_TAG_WIDTH should be 4 bits.
> 
> Why?
> 
> I assume the effect is to save a few flags bits under some
> circumstances?  But that's just me guessing - please fully describe the
> motivation and effects within changelogs.
Ok, I will change the commit message with the "why", and send a v2.

Thanks.