linux-kernel - Re: [PATCH v8 08/14] x86/kasan: KASAN raw shadow memory PTE init

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Message-ID: <2077c91e-0789-4ecc-9560-550d9b1a56d5@gmail.com>
Date: Fri, 16 Jan 2026 14:36:24 +0100
From: Andrey Ryabinin <ryabinin.a.a@...il.com>
To: Maciej Wieczor-Retman <m.wieczorretman@...me>,
 Alexander Potapenko <glider@...gle.com>,
 Andrey Konovalov <andreyknvl@...il.com>, Dmitry Vyukov <dvyukov@...gle.com>,
 Vincenzo Frascino <vincenzo.frascino@....com>,
 Dave Hansen <dave.hansen@...ux.intel.com>, Andy Lutomirski
 <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Thomas Gleixner <tglx@...nel.org>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, x86@...nel.org,
 "H. Peter Anvin" <hpa@...or.com>
Cc: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>,
 kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 08/14] x86/kasan: KASAN raw shadow memory PTE init

On 1/12/26 6:28 PM, Maciej Wieczor-Retman wrote:
> From: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
> 
> In KASAN's generic mode the default value in shadow memory is zero.
> During initialization of shadow memory pages they are allocated and
> zeroed.
> 
> In KASAN's tag-based mode the default tag for the arm64 architecture is
> 0xFE which corresponds to any memory that should not be accessed. On x86
> (where tags are 4-bit wide instead of 8-bit wide) that tag is 0xE so
> during the initializations all the bytes in shadow memory pages should
> be filled with it.
> 
> Use memblock_alloc_try_nid_raw() instead of memblock_alloc_try_nid() to
> avoid zeroing out the memory so it can be set with the KASAN invalid
> tag.
> 
> Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
> Reviewed-by: Alexander Potapenko <glider@...gle.com>
> ---

Reviewed-by: Andrey Ryabinin <ryabinin.a.a@...il.com>