On 26.09.24 17:42, David Hildenbrand wrote:
We should only check for pmd_special() after we made sure that we have a present PMD. For example, if we have a migration PMD, pmd_special() might indicate that we have a special PMD although we really don't. This fixes confusing migration entries as PFN mappings, and not doing what we are supposed to do in the "is_swap_pmd()" case further down in the function -- including messing up COW, page table handling and accounting. Reported-by: syzbot+bf2c35fa302ebe3c7471@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://lore.kernel.org/lkml/66f15c8d.050a0220.c23dd.000f.GAE@xxxxxxxxxx/ Fixes: bc02afbd4d73 ("mm/fork: accept huge pfnmap entries") Cc: Peter Xu <peterx@xxxxxxxxxx> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> --- I yet have to do more testing, but sending this out already.
Testing looks good. Andrew please queue this, it's a rather unpleasent behavior if we fork() with a PMD migration entry that should be fixed upstream soonish :)
(no idea how I could have missed CCing Andrew once more) -- Cheers, David / dhildenb
