linux-kernel - Re: [PATCH v8 14/14] x86/kasan: Make software tag-based kasan available

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Message-ID: <20260113114539.GIaWYwY9q4QuC-J66e@fat_crate.local>
Date: Tue, 13 Jan 2026 12:45:39 +0100
From: Borislav Petkov <bp@...en8.de>
To: Maciej Wieczor-Retman <m.wieczorretman@...me>
Cc: Thomas Gleixner <tglx@...nel.org>, Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, Jonathan Corbet <corbet@....net>,
	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>,
	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	kasan-dev@...glegroups.com
Subject: Re: [PATCH v8 14/14] x86/kasan: Make software tag-based kasan
 available

For all your $Subjects: make sure they have a verb in the name.

For that consult:

https://kernel.org/doc/html/latest/process/maintainer-tip.html#patch-subject

and the following "Changelog" section.

On Mon, Jan 12, 2026 at 05:28:35PM +0000, Maciej Wieczor-Retman wrote:
> From: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>

...

>  Documentation/arch/x86/x86_64/mm.rst | 6 ++++--
>  arch/x86/Kconfig                     | 4 ++++
>  arch/x86/boot/compressed/misc.h      | 1 +
>  arch/x86/include/asm/kasan.h         | 5 +++++
>  arch/x86/mm/kasan_init_64.c          | 6 ++++++
>  lib/Kconfig.kasan                    | 3 ++-
>  6 files changed, 22 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/arch/x86/x86_64/mm.rst b/Documentation/arch/x86/x86_64/mm.rst
> index a6cf05d51bd8..ccbdbb4cda36 100644
> --- a/Documentation/arch/x86/x86_64/mm.rst
> +++ b/Documentation/arch/x86/x86_64/mm.rst
> @@ -60,7 +60,8 @@ Complete virtual memory map with 4-level page tables
>     ffffe90000000000 |  -23    TB | ffffe9ffffffffff |    1 TB | ... unused hole
>     ffffea0000000000 |  -22    TB | ffffeaffffffffff |    1 TB | virtual memory map (vmemmap_base)
>     ffffeb0000000000 |  -21    TB | ffffebffffffffff |    1 TB | ... unused hole
> -   ffffec0000000000 |  -20    TB | fffffbffffffffff |   16 TB | KASAN shadow memory
> +   ffffec0000000000 |  -20    TB | fffffbffffffffff |   16 TB | KASAN shadow memory (generic mode)
> +   fffff40000000000 |   -8    TB | fffffbffffffffff |    8 TB | KASAN shadow memory (software tag-based mode)

These here are non-overlapping ranges. Yours are overlapping. Why?

>    __________________|____________|__________________|_________|____________________________________________________________
>                                                                |
>                                                                | Identical layout to the 56-bit one from here on:
> @@ -130,7 +131,8 @@ Complete virtual memory map with 5-level page tables
>     ffd2000000000000 |  -11.5  PB | ffd3ffffffffffff |  0.5 PB | ... unused hole
>     ffd4000000000000 |  -11    PB | ffd5ffffffffffff |  0.5 PB | virtual memory map (vmemmap_base)
>     ffd6000000000000 |  -10.5  PB | ffdeffffffffffff | 2.25 PB | ... unused hole
> -   ffdf000000000000 |   -8.25 PB | fffffbffffffffff |   ~8 PB | KASAN shadow memory
> +   ffdf000000000000 |   -8.25 PB | fffffbffffffffff |   ~8 PB | KASAN shadow memory (generic mode)
> +   ffeffc0000000000 |   -6    PB | fffffbffffffffff |    4 PB | KASAN shadow memory (software tag-based mode)
>    __________________|____________|__________________|_________|____________________________________________________________
>                                                                |

...

> diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
> index 7f5c11328ec1..3a5577341805 100644
> --- a/arch/x86/mm/kasan_init_64.c
> +++ b/arch/x86/mm/kasan_init_64.c
> @@ -465,4 +465,10 @@ void __init kasan_init(void)
>  
>  	init_task.kasan_depth = 0;
>  	kasan_init_generic();
> +	pr_info("KernelAddressSanitizer initialized\n");

Why?

> +
> +	if (boot_cpu_has(X86_FEATURE_LAM))

cpu_feature_enabled()

> +		kasan_init_sw_tags();
> +	else
> +		pr_info("KernelAddressSanitizer not initialized (sw-tags): hardware doesn't support LAM\n");

You just said "initialized". Now it is not? How about we make up our minds
first and then issue one single true statement?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette