From: Mark Rutland <mark.rutland@arm.com>
To: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: cai@lca.pw, mhocko@suse.com, ira.weiny@intel.com,
david@redhat.com, catalin.marinas@arm.com, will.deacon@arm.com,
linux-kernel@vger.kernel.org, logang@deltatee.com,
james.morse@arm.com, cpandya@codeaurora.org,
arunks@codeaurora.org, akpm@linux-foundation.org,
osalvador@suse.de, mgorman@techsingularity.net,
dan.j.williams@intel.com, linux-arm-kernel@lists.infradead.org,
robin.murphy@arm.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
>
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev 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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190514154000.GA20935@lakrids.cambridge.arm.com \
--to=mark.rutland@arm.com \
--cc=akpm@linux-foundation.org \
--cc=anshuman.khandual@arm.com \
--cc=arunks@codeaurora.org \
--cc=cai@lca.pw \
--cc=catalin.marinas@arm.com \
--cc=cpandya@codeaurora.org \
--cc=dan.j.williams@intel.com \
--cc=david@redhat.com \
--cc=ira.weiny@intel.com \
--cc=james.morse@arm.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=logang@deltatee.com \
--cc=mgorman@techsingularity.net \
--cc=mhocko@suse.com \
--cc=osalvador@suse.de \
--cc=robin.murphy@arm.com \
--cc=will.deacon@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).