linux-kernel - Re: [PATCH v7 02/15] kasan: arm64: x86: Make special tags arch specific

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Message-ID: <aWEF_eJ9Bnn5-8dZ@willie-the-truck>
Date: Fri, 9 Jan 2026 13:43:25 +0000
From: Will Deacon <will@...nel.org>
To: Maciej Wieczor-Retman <m.wieczorretman@...me>
Cc: Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Alexander Potapenko <glider@...gle.com>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Vincenzo Frascino <vincenzo.frascino@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Samuel Holland <samuel.holland@...ive.com>,
	Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>,
	linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
	linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org
Subject: Re: [PATCH v7 02/15] kasan: arm64: x86: Make special tags arch
 specific

On Fri, Jan 09, 2026 at 01:37:49PM +0000, Maciej Wieczor-Retman wrote:
> Hi, and thanks for looking at the patches!
> 
> On 2026-01-08 at 17:56:39 +0000, Will Deacon wrote:
> >On Wed, Dec 10, 2025 at 05:28:43PM +0000, Maciej Wieczor-Retman wrote:
> >> From: Samuel Holland <samuel.holland@...ive.com>
> ...
> >> +#ifdef CONFIG_KASAN_HW_TAGS
> >> +#define KASAN_TAG_MIN		0xF0 /* minimum value for random tags */
> >> +#define KASAN_TAG_WIDTH		4
> >> +#else
> >> +#define KASAN_TAG_WIDTH		8
> >> +#endif
> >
> >Shouldn't this be 0 when KASAN is not in use at all?
> >
> >Will
> 
> This file (as well as the x86 version) gets included in
> include/linux/kasan-tags.h:
> 
> 	#if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS)
> 	#include <asm/kasan-tags.h>
> 	#endif
> 
> 	#ifndef KASAN_TAG_WIDTH
> 	#define KASAN_TAG_WIDTH		0
> 	#endif
> 
> So the 8 or 4 value is only assigned if SW_TAGS or HW_TAGS are enabled.
> Otherwise it's set to zero.

Thanks for the explanation, I'd missed the conditional inclusion of the
arch header.

In which case, the arm64 side looks fine to me:

Acked-by: Will Deacon <will@...nel.org>

Cheers,

Will