On Tue, Dec 06, 2022 at 06:16:07PM +0100, Jann Horn wrote:
commit 2ba99c5e08812494bc57f319fb562f527d9bacd8 upstream.
Since commit 70cbc3cc78a99 ("mm: gup: fix the fast GUP race against THP
collapse"), the lockless_pages_from_mm() fastpath rechecks the pmd_t to
ensure that the page table was not removed by khugepaged in between.
However, lockless_pages_from_mm() still requires that the page table is
not concurrently freed. Fix it by sending IPIs (if the architecture uses
semi-RCU-style page table freeing) before freeing/reusing page tables.
Link: https://lkml.kernel.org/r/20221129154730.2274278-2-jannh@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20221128180252.1684965-2-jannh@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20221125213714.4115729-2-jannh@xxxxxxxxxx
Fixes: ba76149f47d8 ("thp: khugepaged")
Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
Reviewed-by: Yang Shi <shy828301@xxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
[manual backport: two of the three places in khugepaged that can free
ptes were refactored into a common helper between 5.15 and 6.0;
TLB flushing was refactored between 5.4 and 5.10;
TLB flushing was refactored between 4.19 and 5.4;
pmd collapse for PTE-mapped THP was only added in 5.4]
Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
This one actually fails on v4.19:
mm/khugepaged.c: In function 'collapse_huge_page':
mm/khugepaged.c:1048:9: error: implicit declaration of function 'tlb_remove_table_sync_one'; did you mean 'tlb_remove_page_size'? [-Werror=implicit-function-declaration]
1048 | tlb_remove_table_sync_one();
| ^~~~~~~~~~~~~~~~~~~~~~~~~
| tlb_remove_page_size
Presumably because we don't have 9de7d833e370 ("s390/tlb: Convert to
generic mmu_gather") on those kernels.
I'll drop both backports from <= 4.19 kernels.
--
Thanks,
Sasha
