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From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, akpm@linux-foundation.org,
	catalin.marinas@arm.com, will.deacon@arm.com,
	mark.rutland@arm.com, ira.weiny@intel.com, david@redhat.com,
	cai@lca.pw, logang@deltatee.com, james.morse@arm.com,
	cpandya@codeaurora.org, arunks@codeaurora.org,
	dan.j.williams@intel.com, mgorman@techsingularity.net,
	osalvador@suse.de, ard.biesheuvel@arm.com
Subject: Re: [PATCH V4 3/4] arm64/mm: Hold memory hotplug lock while walking for kernel page table dump
Date: Fri, 24 May 2019 10:22:18 +0530	[thread overview]
Message-ID: <4a9e0e2a-2acd-11b5-5181-41801cd11d98@arm.com> (raw)
In-Reply-To: <20190521101457.GK32329@dhcp22.suse.cz>



On 05/21/2019 03:44 PM, Michal Hocko wrote:
> On Mon 20-05-19 10:48:35, Anshuman Khandual wrote:
>> The arm64 page table dump code can race with concurrent modification of the
>> kernel page tables. When a leaf entries are modified concurrently, the dump
>> code may log stale or inconsistent information for a VA range, but this is
>> otherwise not harmful.
>>
>> When intermediate levels of table are freed, the dump code will continue to
>> use memory which has been freed and potentially reallocated for another
>> purpose. In such cases, the dump code may dereference bogus addresses,
>> leading to a number of potential problems.
>>
>> Intermediate levels of table may by freed during memory hot-remove,
>> which will be enabled by a subsequent patch. To avoid racing with
>> this, take the memory hotplug lock when walking the kernel page table.
> 
> I've had a comment on this patch in the previous version which didn't
> get answered completely AFAICS. If you really insist then please make
> sure to describe why does this really matter because this will make
> any further changes to the hotplug locking harder and I would to see
> that it is worth the additional trouble.

Hello Michal,

I was under the impression (seems wrongful now) that the previous discussion
was complete. Nonetheless we can still discuss it further. Mark has responded
on the previous V3 thread [1] and because this particular patch does not have
any changes from last time, we can continue discussing this in that thread.

[1] https://lkml.org/lkml/2019/5/22/613   

- Anshuman

  reply	other threads:[~2019-05-24  4:53 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-20  5:18 [PATCH V4 0/4] arm64/mm: Enable memory hot remove Anshuman Khandual
2019-05-20  5:18 ` [PATCH V4 1/4] mm/hotplug: Reorder arch_remove_memory() call in __remove_memory() Anshuman Khandual
2019-05-20  5:18 ` [PATCH V4 2/4] arm64/mm: Inhibit huge-vmap with ptdump Anshuman Khandual
2019-05-20  5:18 ` [PATCH V4 3/4] arm64/mm: Hold memory hotplug lock while walking for kernel page table dump Anshuman Khandual
2019-05-21 10:14   ` Michal Hocko
2019-05-24  4:52     ` Anshuman Khandual [this message]
2019-05-20  5:18 ` [PATCH V4 4/4] arm64/mm: Enable memory hot remove Anshuman Khandual
2019-05-21 10:20   ` David Hildenbrand
2019-05-27  8:09     ` Anshuman Khandual
2019-05-27 10:21       ` David Hildenbrand
2019-05-27 10:21       ` David Hildenbrand

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