From: Will Deacon <will@kernel.org>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: "David Hildenbrand" <david@redhat.com>,
"Anshuman Khandual" <anshuman.khandual@arm.com>,
"Mark Rutland" <mark.rutland@arm.com>,
linux-kernel@vger.kernel.org,
"Mike Rapoport" <rppt@linux.ibm.com>,
linux-mm@kvack.org, "Jérôme Glisse" <jglisse@redhat.com>,
"James Morse" <james.morse@arm.com>,
"Dan Williams" <dan.j.williams@intel.com>,
"Robin Murphy" <robin.murphy@arm.com>,
"Ard Biesheuvel" <ardb@kernel.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH V2 1/2] arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory
Date: Wed, 3 Mar 2021 21:24:07 +0000 [thread overview]
Message-ID: <20210303212406.GB20055@willie-the-truck> (raw)
In-Reply-To: <20210303190428.GB24035@arm.com>
On Wed, Mar 03, 2021 at 07:04:33PM +0000, Catalin Marinas wrote:
> On Thu, Feb 11, 2021 at 01:35:56PM +0100, David Hildenbrand wrote:
> > On 11.02.21 13:10, Anshuman Khandual wrote:
> > > On 2/11/21 5:23 PM, Will Deacon wrote:
> > > > ... and dropped. These patches appear to be responsible for a boot
> > > > regression reported by CKI:
> > >
> > > Ahh, boot regression ? These patches only change the behaviour
> > > for non boot memory only.
> > >
> > > > https://lore.kernel.org/r/cki.8D1CB60FEC.K6NJMEFQPV@redhat.com
> > >
> > > Will look into the logs and see if there is something pointing to
> > > the problem.
> >
> > It's strange. One thing I can imagine is a mis-detection of early sections.
> > However, I don't see that happening:
> >
> > In sparse_init_nid(), we:
> > 1. Initialize the memmap
> > 2. Set SECTION_IS_EARLY | SECTION_HAS_MEM_MAP via
> > sparse_init_one_section()
> >
> > Only hotplugged sections (DIMMs, dax/kmem) set SECTION_HAS_MEM_MAP without
> > SECTION_IS_EARLY - which is correct, because these are not early.
> >
> > So once we know that we have valid_section() -- SECTION_HAS_MEM_MAP is set
> > -- early_section() should be correct.
> >
> > Even if someone would be doing a pfn_valid() after
> > memblocks_present()->memory_present() but before
> > sparse_init_nid(), we should be fine (!valid_section() -> return 0).
>
> I couldn't figure out how this could fail with Anshuman's patches.
> Will's suspicion is that some invalid/null pointer gets dereferenced
> before being initialised but the only case I see is somewhere in
> pfn_section_valid() (ms->usage) if valid_section() && !early_section().
>
> Assuming that we do get a valid_section(ms) && !early_section(ms), is
> there a case where ms->usage is not initialised? I guess races with
> section_deactivate() are not possible this early.
>
> Another situation could be that pfn_valid() returns true when no memory
> is mapped for that pfn.
The case I wondered about was __pfn_to_section() with a bogus pfn, since
with patch 2/2 we call that *before* checking that pfn_to_section_nr() is
sane.
Will
next prev parent reply other threads:[~2021-03-03 21:24 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-02 4:11 [PATCH V2 0/2] arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory Anshuman Khandual
2021-02-02 4:11 ` [PATCH V2 1/2] " Anshuman Khandual
2021-02-02 12:32 ` Will Deacon
2021-02-02 12:35 ` Will Deacon
2021-02-02 12:39 ` David Hildenbrand
2021-02-02 12:51 ` Will Deacon
2021-02-02 12:56 ` David Hildenbrand
2021-02-03 3:50 ` Anshuman Khandual
2021-02-05 18:55 ` Will Deacon
2021-02-11 11:53 ` Will Deacon
2021-02-11 12:10 ` Anshuman Khandual
2021-02-11 12:21 ` Will Deacon
2021-02-11 12:35 ` David Hildenbrand
2021-03-03 19:04 ` Catalin Marinas
2021-03-03 19:24 ` David Hildenbrand
2021-03-03 21:24 ` Will Deacon [this message]
2021-03-04 3:31 ` Anshuman Khandual
2021-03-04 8:12 ` David Hildenbrand
2021-03-04 9:36 ` Will Deacon
2021-03-05 4:22 ` Anshuman Khandual
2021-02-02 4:11 ` [PATCH V2 2/2] arm64/mm: Reorganize pfn_valid() Anshuman Khandual
2021-02-02 8:26 ` David Hildenbrand
2021-02-05 18:52 ` [PATCH V2 0/2] arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory Will Deacon
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