The patch titled Subject: mm, page_alloc: check pfn is valid before moving to freelist has been added to the -mm tree. Its filename is mm-page_alloc-check-pfn-is-valid-before-moving-to-freelist.patch
This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/mm-page_alloc-check-pfn-is-valid-b... and later at https://ozlabs.org/~akpm/mmotm/broken-out/mm-page_alloc-check-pfn-is-valid-b...
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------------------------------------------------------ From: Sudarshan Rajagopalan quic_sudaraja@quicinc.com Subject: mm, page_alloc: check pfn is valid before moving to freelist
Check if pfn is valid before or not before moving it to freelist.
There are possible scenario where a pageblock can have partial physical hole and partial part of System RAM. This happens when base address in RAM partition table is not aligned to pageblock size.
Example:
Say we have this first two entries in RAM partition table -
Base Addr: 0x0000000080000000 Length: 0x0000000058000000 Base Addr: 0x00000000E3930000 Length: 0x0000000020000000 ...
Physical hole: 0xD8000000 - 0xE3930000
On system having 4K as page size and hence pageblock size being 4MB, the base address 0xE3930000 is not aligned to 4MB pageblock size.
Now we will have pageblock which has partial physical hole and partial part of System RAM -
Pageblock [0xE3800000 - 0xE3C00000] - 0xE3800000 - 0xE3930000 -- physical hole 0xE3930000 - 0xE3C00000 -- System RAM
Now doing __alloc_pages say we get a valid page with PFN 0xE3B00 from __rmqueue_fallback, we try to put other pages from the same pageblock as well into freelist by calling steal_suitable_fallback().
We then search for freepages from start of the pageblock due to below code -
move_freepages_block(zone, page, migratetype, ...) { pfn = page_to_pfn(page); start_pfn = pfn & ~(pageblock_nr_pages - 1); end_pfn = start_pfn + pageblock_nr_pages - 1; ... }
With the pageblock which has partial physical hole at the beginning, we will run into PFNs from the physical hole whose struct page is not initialized and is invalid, and system would crash as we operate on invalid struct page to find out of page is in Buddy or LRU or not
[ 107.629453][ T9688] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 [ 107.639214][ T9688] Mem abort info: [ 107.642829][ T9688] ESR = 0x96000006 [ 107.646696][ T9688] EC = 0x25: DABT (current EL), IL = 32 bits [ 107.652878][ T9688] SET = 0, FnV = 0 [ 107.656751][ T9688] EA = 0, S1PTW = 0 [ 107.660705][ T9688] FSC = 0x06: level 2 translation fault [ 107.666455][ T9688] Data abort info: [ 107.670151][ T9688] ISV = 0, ISS = 0x00000006 [ 107.674827][ T9688] CM = 0, WnR = 0 [ 107.678615][ T9688] user pgtable: 4k pages, 39-bit VAs, pgdp=000000098a237000 [ 107.685970][ T9688] [0000000000000000] pgd=0800000987170003, p4d=0800000987170003, pud=0800000987170003, pmd=0000000000000000 [ 107.697582][ T9688] Internal error: Oops: 96000006 [#1] PREEMPT SMP
[ 108.209839][ T9688] pc : move_freepages_block+0x174/0x27c [ 108.215407][ T9688] lr : steal_suitable_fallback+0x20c/0x398
[ 108.305908][ T9688] Call trace: [ 108.309151][ T9688] move_freepages_block+0x174/0x27c [PageLRU] [ 108.314359][ T9688] steal_suitable_fallback+0x20c/0x398 [ 108.319826][ T9688] rmqueue_bulk+0x250/0x934 [ 108.324325][ T9688] rmqueue_pcplist+0x178/0x2ac [ 108.329086][ T9688] rmqueue+0x5c/0xc10 [ 108.333048][ T9688] get_page_from_freelist+0x19c/0x430 [ 108.338430][ T9688] __alloc_pages+0x134/0x424 [ 108.343017][ T9688] page_cache_ra_unbounded+0x120/0x324 [ 108.348494][ T9688] do_sync_mmap_readahead+0x1b0/0x234 [ 108.353878][ T9688] filemap_fault+0xe0/0x4c8 [ 108.358375][ T9688] do_fault+0x168/0x6cc [ 108.362518][ T9688] handle_mm_fault+0x5c4/0x848 [ 108.367280][ T9688] do_page_fault+0x3fc/0x5d0 [ 108.371867][ T9688] do_translation_fault+0x6c/0x1b0 [ 108.376985][ T9688] do_mem_abort+0x68/0x10c [ 108.381389][ T9688] el0_ia+0x50/0xbc [ 108.385175][ T9688] el0t_32_sync_handler+0x88/0xbc [ 108.390208][ T9688] el0t_32_sync+0x1b8/0x1bc
Hence, avoid operating on invalid pages within the same pageblock by checking if pfn is valid or not.
Link: https://lkml.kernel.org/r/fb3c8c008994b2ed96f74b6b9698ff998b689bd2.164979405... Signed-off-by: Sudarshan Rajagopalan quic_sudaraja@quicinc.com Fixes: 859a85ddf90e7140 ("mm: remove pfn_valid_within() and CONFIG_HOLES_IN_ZONE") Cc: Mike Rapoport rppt@linux.ibm.com Cc: Anshuman Khandual anshuman.khandual@arm.com Cc: Suren Baghdasaryan surenb@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
--- a/mm/page_alloc.c~mm-page_alloc-check-pfn-is-valid-before-moving-to-freelist +++ a/mm/page_alloc.c @@ -2521,6 +2521,11 @@ static int move_freepages(struct zone *z int pages_moved = 0;
for (pfn = start_pfn; pfn <= end_pfn;) { + if (!pfn_valid(pfn)) { + pfn++; + continue; + } + page = pfn_to_page(pfn); if (!PageBuddy(page)) { /* _
Patches currently in -mm which might be from quic_sudaraja@quicinc.com are
mm-page_alloc-check-pfn-is-valid-before-moving-to-freelist.patch