linux-kernel - Re: [PATCH 04/13] powerpc: Disable CONFIG_DCACHE_WORD

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Date:   Thu, 14 Dec 2023 08:42:06 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Nicholas Miehlbradt <nicholas@...ux.ibm.com>,
        "glider@...gle.com" <glider@...gle.com>,
        "elver@...gle.com" <elver@...gle.com>,
        "dvyukov@...gle.com" <dvyukov@...gle.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>,
        "npiggin@...il.com" <npiggin@...il.com>
CC:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "kasan-dev@...glegroups.com" <kasan-dev@...glegroups.com>,
        "iii@...ux.ibm.com" <iii@...ux.ibm.com>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/13] powerpc: Disable CONFIG_DCACHE_WORD_ACCESS when
 KMSAN is enabled



Le 14/12/2023 à 06:55, Nicholas Miehlbradt a écrit :
> Word sized accesses may read uninitialized data when optimizing loads.
> Disable this optimization when KMSAN is enabled to prevent false
> positives.
> 
> Signed-off-by: Nicholas Miehlbradt <nicholas@...ux.ibm.com>
> ---
>   arch/powerpc/Kconfig | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 6f105ee4f3cf..e33e3250c478 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -182,7 +182,7 @@ config PPC
>   	select BUILDTIME_TABLE_SORT
>   	select CLONE_BACKWARDS
>   	select CPUMASK_OFFSTACK			if NR_CPUS >= 8192
> -	select DCACHE_WORD_ACCESS		if PPC64 && CPU_LITTLE_ENDIAN
> +	select DCACHE_WORD_ACCESS		if PPC64 && CPU_LITTLE_ENDIAN && !KMSAN
>   	select DMA_OPS_BYPASS			if PPC64
>   	select DMA_OPS				if PPC64
>   	select DYNAMIC_FTRACE			if FUNCTION_TRACER


Seems like all archs do this. Maybe a better approach would be to define 
a HAVE_DCACHE_WORD_ACCESS that is selected by arches, and then the core 
part select DCACHE_WORD_ACCESS when HAVE_DCACHE_WORD_ACCESS && !KMSAN

Christophe