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From:   Alexander Potapenko <glider@google.com>
Date:   Mon, 11 Dec 2023 11:26:16 +0100
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Subject: Re: [PATCH v2 32/33] s390: Implement the architecture-specific kmsan functions
To:     Ilya Leoshkevich <iii@linux.ibm.com>
Cc:     Alexander Gordeev <agordeev@linux.ibm.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>
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> +static inline void *arch_kmsan_get_meta_or_null(void *addr, bool is_origin)
> +{
> +       if (addr >= (void *)&S390_lowcore &&
> +           addr < (void *)(&S390_lowcore + 1)) {
> +               /*
> +                * Different lowcores accessed via S390_lowcore are described
> +                * by the same struct page. Resolve the prefix manually in
> +                * order to get a distinct struct page.
> +                */
> +               addr += (void *)lowcore_ptr[raw_smp_processor_id()] -
> +                       (void *)&S390_lowcore;
> +               return kmsan_get_metadata(addr, is_origin);
> +       }
> +       return NULL;
> +}

Is there a possibility for infinite recursion here? E.g. can
`lowcore_ptr[raw_smp_processor_id()]` point somewhere in between
`(void *)&S390_lowcore` and `(void *)(&S390_lowcore + 1))`?