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Date: Thu, 21 Dec 2023 13:14:17 +0100
From: Alexander Gordeev <agordeev@linux.ibm.com>
To: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Alexander Potapenko <glider@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christoph Lameter <cl@linux.com>, David Rientjes <rientjes@google.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>, Marco Elver <elver@google.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Pekka Enberg <penberg@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Vasily Gorbik <gor@linux.ibm.com>, Vlastimil Babka <vbabka@suse.cz>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>, kasan-dev@googlegroups.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-s390@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
        Mark Rutland <mark.rutland@arm.com>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Sven Schnelle <svens@linux.ibm.com>
Subject: Re: [PATCH v3 28/34] s390/mm: Define KMSAN metadata for vmalloc and
 modules
Message-ID: <ZYQsGbr7HlQjlJRs@li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com>
References: <20231213233605.661251-1-iii@linux.ibm.com>
 <20231213233605.661251-29-iii@linux.ibm.com>
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In-Reply-To: <20231213233605.661251-29-iii@linux.ibm.com>

On Thu, Dec 14, 2023 at 12:24:48AM +0100, Ilya Leoshkevich wrote:
> The pages for the KMSAN metadata associated with most kernel mappings
> are taken from memblock by the common code. However, vmalloc and module
> metadata needs to be defined by the architectures.
> 
> Be a little bit more careful than x86: allocate exactly MODULES_LEN
> for the module shadow and origins, and then take 2/3 of vmalloc for
> the vmalloc shadow and origins. This ensures that users passing small
> vmalloc= values on the command line do not cause module metadata
> collisions.
> 
> Reviewed-by: Alexander Potapenko <glider@google.com>
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
>  arch/s390/boot/startup.c        |  8 ++++++++
>  arch/s390/include/asm/pgtable.h | 10 ++++++++++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/arch/s390/boot/startup.c b/arch/s390/boot/startup.c
> index 8104e0e3d188..e37e7ffda430 100644
> --- a/arch/s390/boot/startup.c
> +++ b/arch/s390/boot/startup.c
> @@ -253,9 +253,17 @@ static unsigned long setup_kernel_memory_layout(void)
>  	MODULES_END = round_down(__abs_lowcore, _SEGMENT_SIZE);
>  	MODULES_VADDR = MODULES_END - MODULES_LEN;
>  	VMALLOC_END = MODULES_VADDR;
> +#ifdef CONFIG_KMSAN
> +	VMALLOC_END -= MODULES_LEN * 2;
> +#endif
>  
>  	/* allow vmalloc area to occupy up to about 1/2 of the rest virtual space left */
>  	vmalloc_size = min(vmalloc_size, round_down(VMALLOC_END / 2, _REGION3_SIZE));

Since commit 2a65c6e1ad06 ("s390/boot: always align vmalloc area on segment boundary")
vmalloc_size is aligned on _SEGMENT_SIZE boundary.

> +#ifdef CONFIG_KMSAN
> +	/* take 2/3 of vmalloc area for KMSAN shadow and origins */
> +	vmalloc_size = round_down(vmalloc_size / 3, _REGION3_SIZE);

And thus, the alignment here should be _SEGMENT_SIZE as well.

> +	VMALLOC_END -= vmalloc_size * 2;
> +#endif
>  	VMALLOC_START = VMALLOC_END - vmalloc_size;
>  
>  	/* split remaining virtual space between 1:1 mapping & vmemmap array */

...

With the above fixup:
Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>

Thanks!