linux-kernel - Re: [PATCH 26/32] s390/mm: Define KMSAN metadata for vmalloc and modules

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Date:   Fri, 17 Nov 2023 17:41:56 +0100
From:   Alexander Gordeev <agordeev@...ux.ibm.com>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     Ilya Leoshkevich <iii@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.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 26/32] s390/mm: Define KMSAN metadata for vmalloc and
 modules

On Thu, Nov 16, 2023 at 04:03:13PM +0100, Alexander Potapenko wrote:

Hi Alexander!

> >         /* 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));
> > +#ifdef CONFIG_KMSAN
> > +       /* take 2/3 of vmalloc area for KMSAN shadow and origins */
> > +       vmalloc_size = round_down(vmalloc_size / 3, PAGE_SIZE);
> Is it okay that vmalloc_size is only aligned on PAGE_SIZE?
> E.g. above the alignment is _REGION3_SIZE.

Good question!

This patch does not break anything, although the _REGION3_SIZE 
alignment would be consistent here. Yet, we might rethink this
whole code piece and the next version would reflect that.

Thanks!