[V5,2/3] arm64/mm: Hold memory hotplug lock while walking for kernel page table dump
diff mbox series

Message ID 1559121387-674-3-git-send-email-anshuman.khandual@arm.com
State New
Headers show
Series
  • arm64/mm: Enable memory hot remove
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Commit Message

Anshuman Khandual May 29, 2019, 9:16 a.m. UTC
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.

Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
 arch/arm64/mm/ptdump_debugfs.c | 3 +++
 1 file changed, 3 insertions(+)

Comments

Mark Rutland May 30, 2019, 10:42 a.m. UTC | #1
On Wed, May 29, 2019 at 02:46:26PM +0530, 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.
> 
> Acked-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
>  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();

We need to explicitly include <linux/memory_hotplug.h> to get the
prototypes of {get,put}_online_mems().

With that fixed up:

Acked-by: Mark Rutland <mark.rutland@arm.com>

I understand from [1] that Michal is ok with using these here, and we're
open to reworking this if/when the hotplug locking is changed.

Mark.

[1] https://lkml.kernel.org/r/20190527072001.GB1658@dhcp22.suse.cz

>  	return 0;
>  }
>  DEFINE_SHOW_ATTRIBUTE(ptdump);
> -- 
> 2.7.4
>

Patch
diff mbox series

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);