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From: Mark Rutland <mark.rutland@arm.com>
To: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, akpm@linux-foundation.org,
	catalin.marinas@arm.com, will.deacon@arm.com, mhocko@suse.com,
	mgorman@techsingularity.net, james.morse@arm.com,
	robin.murphy@arm.com, cpandya@codeaurora.org,
	arunks@codeaurora.org, dan.j.williams@intel.com,
	osalvador@suse.de, david@redhat.com, cai@lca.pw,
	logang@deltatee.com, ira.weiny@intel.com
Subject: Re: [PATCH V3 2/4] arm64/mm: Hold memory hotplug lock while walking for kernel page table dump
Date: Tue, 14 May 2019 16:40:00 +0100	[thread overview]
Message-ID: <20190514154000.GA20935@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <1557824407-19092-3-git-send-email-anshuman.khandual@arm.com>

On Tue, May 14, 2019 at 02:30:05PM +0530, Anshuman Khandual wrote:
> The arm64 pagetable 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 addressses,
> leading to a number of potential problems.
> 
> Intermediate levels of table may by freed during memory hot-remove, or when
> installing a huge mapping in the vmalloc region. To avoid racing with these
> cases, take the memory hotplug lock when walking the kernel page table.
> 
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>

Can we please move this after the next patch (which addresses the huge
vmap case), and change the last paragraph to:

  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.

With that, this looks good to me.

Thanks,
Mark.

> ---
>  arch/arm64/mm/ptdump_debugfs.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm64/mm/ptdump_debugfs.c b/arch/arm64/mm/ptdump_debugfs.c
> index 064163f..80171d1 100644
> --- a/arch/arm64/mm/ptdump_debugfs.c
> +++ b/arch/arm64/mm/ptdump_debugfs.c
> @@ -7,7 +7,10 @@
>  static int ptdump_show(struct seq_file *m, void *v)
>  {
>  	struct ptdump_info *info = m->private;
> +
> +	get_online_mems();
>  	ptdump_walk_pgd(m, info);
> +	put_online_mems();
>  	return 0;
>  }
>  DEFINE_SHOW_ATTRIBUTE(ptdump);
> -- 
> 2.7.4
> 

  parent reply	other threads:[~2019-05-14 15:40 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-14  9:00 [PATCH V3 0/4] arm64/mm: Enable memory hot remove Anshuman Khandual
2019-05-14  9:00 ` [PATCH V3 1/4] mm/hotplug: Reorder arch_remove_memory() call in __remove_memory() Anshuman Khandual
2019-05-14  9:05   ` David Hildenbrand
2019-05-14  9:00 ` [PATCH V3 2/4] arm64/mm: Hold memory hotplug lock while walking for kernel page table dump Anshuman Khandual
2019-05-14  9:16   ` David Hildenbrand
2019-05-14 15:40   ` Mark Rutland [this message]
2019-05-15  1:56     ` Anshuman Khandual
2019-05-15 16:58   ` Michal Hocko
2019-05-16 10:23     ` Mark Rutland
2019-05-16 11:05       ` Michal Hocko
2019-05-22 16:42         ` Mark Rutland
2019-05-24  6:06           ` Anshuman Khandual
2019-05-27  7:20           ` Michal Hocko
2019-05-28 14:09             ` Mark Rutland
2019-05-16 11:06       ` Anshuman Khandual
2019-05-16 11:16         ` Michal Hocko
2019-05-23  8:40           ` David Hildenbrand
2019-05-24  5:43             ` Anshuman Khandual
2019-05-14  9:00 ` [PATCH V3 3/4] arm64/mm: Inhibit huge-vmap with ptdump Anshuman Khandual
2019-05-14  9:20   ` David Hildenbrand
2019-05-16  8:38   ` Ard Biesheuvel
2019-05-14  9:00 ` [PATCH V3 4/4] arm64/mm: Enable memory hot remove Anshuman Khandual
2019-05-14  9:08   ` David Hildenbrand
2019-05-15 11:49   ` Mark Rutland
2019-05-16  5:34     ` Anshuman Khandual
2019-05-16 10:57       ` Mark Rutland
2019-05-17  3:15         ` Anshuman Khandual
2019-05-14  9:10 ` [PATCH V3 0/4] " David Hildenbrand

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