On 14.05.19 11:00, 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.khand...@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();
The name of that function is somewhat stale now, it used to refer to
online/offlining of pages only. The underlying lock is the
mem_hotplug_lock. Maybe we should rename that function some day ...
> ptdump_walk_pgd(m, info);
> + put_online_mems();
> return 0;
Acked-by: David Hildenbrand <da...@redhat.com>
> }
> DEFINE_SHOW_ATTRIBUTE(ptdump);
>
--
Thanks,
David / dhildenb
