Re: [PATCH V3 2/4] arm64/mm: Hold memory hotplug lock while walking for kernel page table dump
From: Anshuman Khandual
Date: Tue May 14 2019 - 21:58:17 EST
On 05/14/2019 09:10 PM, Mark Rutland wrote:
> 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@xxxxxxx>
> 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.
Sure will do.