linux-kernel - Re: [PATCH v4 10/45] libnvdimm/pfn_dev: increase MAX_STRUCT_PAGE

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Message-ID: <63d8130c30bb5_ea22229489@dwillia2-xfh.jf.intel.com.notmuch>
Date:   Mon, 30 Jan 2023 10:57:16 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Alexander Potapenko <glider@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>
CC:     Marco Elver <elver@...gle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        "Andy Lutomirski" <luto@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Borislav Petkov <bp@...en8.de>, Christoph Hellwig <hch@....de>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "Ilya Leoshkevich" <iii@...ux.ibm.com>,
        Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Kees Cook <keescook@...omium.org>,
        Mark Rutland <mark.rutland@....com>,
        Matthew Wilcox <willy@...radead.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Pekka Enberg <penberg@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 10/45] libnvdimm/pfn_dev: increase MAX_STRUCT_PAGE_SIZE

Alexander Potapenko wrote:
[..]
> >
> > diff --git a/drivers/nvdimm/Kconfig b/drivers/nvdimm/Kconfig
> > index 79d93126453d..5693869b720b 100644
> > --- a/drivers/nvdimm/Kconfig
> > +++ b/drivers/nvdimm/Kconfig
> > @@ -63,6 +63,7 @@ config NVDIMM_PFN
> >         bool "PFN: Map persistent (device) memory"
> >         default LIBNVDIMM
> >         depends on ZONE_DEVICE
> > +       depends on !KMSAN
> >         select ND_CLAIM
> >         help
> >           Map persistent memory, i.e. advertise it to the memory
> >
> 
> Looks like we still don't have a resolution for this problem.
> I have the following options in mind:
> 
> 1. Set MAX_STRUCT_PAGE_SIZE to 80 (i.e. increase it by 2*sizeof(struct
> page *) added by KMSAN) instead of 128.
> 2. Disable storing of struct pages on device for KMSAN builds.
> 
> , but if those are infeasible, we can always go for:
> 
> 3. Disable KMSAN for NVDIMM and reflect it in Documentation. I am
> happy to send the patch if we decide this is the best option.

I copied you on the new proposal here:

https://lore.kernel.org/nvdimm/167467815773.463042.7022545814443036382.stgit@dwillia2-xfh.jf.intel.com/

It disables PMEM namespace creation with page-array reservations when
sizeof(struct page) > 64.

Note, it was pre-existing behavior for PMEM namespaces with too small of
a reservation to fail to enable. That gives me confidence that the
restriction to lose some PMEM namespace access with these memory debug
facilities is acceptable.