Re: [PATCH 2/2] base/memory, hotplug: fix a kernel oops in show_valid_zones()
From: Kani, Toshimitsu
Date: Thu Jan 26 2017 - 17:44:50 EST
On Thu, 2017-01-26 at 13:52 -0800, Andrew Morton wrote:
> On Thu, 26 Jan 2017 14:44:15 -0700 Toshi Kani <toshi.kani@xxxxxxx>
> > Reading a sysfs memoryN/valid_zones file leads to the following
> > oops when the first page of a range is not backed by struct page.
> > show_valid_zones() assumes that 'start_pfn' is always valid for
> > page_zone().
> > ÂBUG: unable to handle kernel paging request at ffffea017a000000
> > ÂIP: show_valid_zones+0x6f/0x160
> > Since test_pages_in_a_zone() already checks holes, extend this
> > function to return 'valid_start' and 'valid_end' for a given range.
> > show_valid_zones() then proceeds with the valid range.
> This doesn't apply to current mainline due to changes in
> zone_can_shift().ÂÂPlease redo and resend.
Sorry, I will rebase to the -mm tree and resend the patches.
> Please also update the changelog to provide sufficient information
> for others to decide which kernel(s) need the fix.ÂÂIn particular:
> under what circumstances will it occur?ÂÂOn real machines which real
> people own?
Yes, this issue happens on real x86 machines with 64GiB or more memory.
On such systems, the memory block size is bumped up to 2GiB. 
Here is an example system. 0x3240000000 is only aligned by 1GiB and
its memory block starts from 0x3200000000, which is not backed by
ÂBIOS-e820: [memÂ0x0000003240000000-0x000000603fffffff] usable
I will add the descriptions to the patch.