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Message-ID: <ZnP1dwNycehZyjkQ@li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com>
Date: Thu, 20 Jun 2024 11:25:11 +0200
From: Alexander Gordeev <agordeev@...ux.ibm.com>
To: Ilya Leoshkevich <iii@...ux.ibm.com>
Cc: Alexander Potapenko <glider@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Christoph Lameter <cl@...ux.com>, David Rientjes <rientjes@...gle.com>,
Heiko Carstens <hca@...ux.ibm.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>, Marco Elver <elver@...gle.com>,
Masami Hiramatsu <mhiramat@...nel.org>,
Pekka Enberg <penberg@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>,
Vasily Gorbik <gor@...ux.ibm.com>, Vlastimil Babka <vbabka@...e.cz>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Hyeonggon Yoo <42.hyeyoo@...il.com>, kasan-dev@...glegroups.com,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
linux-s390@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
Mark Rutland <mark.rutland@....com>,
Roman Gushchin <roman.gushchin@...ux.dev>,
Sven Schnelle <svens@...ux.ibm.com>
Subject: Re: [PATCH v5 36/37] s390/kmsan: Implement the architecture-specific
functions
On Wed, Jun 19, 2024 at 05:44:11PM +0200, Ilya Leoshkevich wrote:
Hi Ilya,
> +static inline bool is_lowcore_addr(void *addr)
> +{
> + return addr >= (void *)&S390_lowcore &&
> + addr < (void *)(&S390_lowcore + 1);
> +}
> +
> +static inline void *arch_kmsan_get_meta_or_null(void *addr, bool is_origin)
> +{
> + if (is_lowcore_addr(addr)) {
> + /*
> + * 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;
If I am not mistaken neither raw_smp_processor_id() itself, nor
lowcore_ptr[raw_smp_processor_id()] are atomic. Should the preemption
be disabled while the addr is calculated?
But then the question arises - how meaningful the returned value is?
AFAICT kmsan_get_metadata() is called from a preemptable context.
So if the CPU is changed - how useful the previous CPU lowcore meta is?
Is it a memory block that needs to be ignored instead?
> + if (WARN_ON_ONCE(is_lowcore_addr(addr)))
> + return NULL;
lowcore_ptr[] pointing into S390_lowcore is rather a bug.
> + return kmsan_get_metadata(addr, is_origin);
> + }
> + return NULL;
> +}
Thanks!
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