linux-kernel - Re: [PATCH v6 14/18] x86: Minimal SLAB alignment

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Message-ID: <wzxmteswfsj3idgwyai7m3ou7kulfmxerxkq56xfhoqhvpz3tq@omy5z7eb3esp>
Date: Tue, 18 Nov 2025 11:36:54 +0000
From: Maciej Wieczor-Retman <m.wieczorretman@...me>
To: Alexander Potapenko <glider@...gle.com>
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Subject: Re: [PATCH v6 14/18] x86: Minimal SLAB alignment

On 2025-11-10 at 18:48:35 +0100, Alexander Potapenko wrote:
>> diff --git a/arch/x86/include/asm/cache.h b/arch/x86/include/asm/cache.h
>> index 69404eae9983..3232583b5487 100644
>> --- a/arch/x86/include/asm/cache.h
>> +++ b/arch/x86/include/asm/cache.h
>> @@ -21,4 +21,8 @@
>>  #endif
>>  #endif
>>
>> +#ifdef CONFIG_KASAN_SW_TAGS
>> +#define ARCH_SLAB_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT)
>
>I don't think linux/linkage.h (the only header included here) defines
>KASAN_SHADOW_SCALE_SHIFT, does it?

I revised all the x86 and non-arch places where ARCH_SLAB_MINALIGN is used and
all these places also include linux/slab.h which does include
KASAN_SHADOW_SCALE_SHIFT. So there are no cases where it's undefined.

The minalign makes sense defined here but including kasan headers causes
compilation errors all over the place. And I don't think moving
KASAN_SHADOW_SCALE_SHIFT here makes much sense?