Re: [PATCH stable 4.19 1/2] mm/khugepaged: fix GUP-fast interaction by sending IPI

[Sasha Levin <sashal@kernel.org>]

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@google.com
>Link: https://lkml.kernel.org/r/20221128180252.1684965-2-jannh@google.com
>Link: https://lkml.kernel.org/r/20221125213714.4115729-2-jannh@google.com
>Fixes: ba76149f47d8 ("thp: khugepaged")
>Signed-off-by: Jann Horn <jannh@google.com>
>Reviewed-by: Yang Shi <shy828301@gmail.com>
>Acked-by: David Hildenbrand <david@redhat.com>
>Cc: John Hubbard <jhubbard@nvidia.com>
>Cc: Peter Xu <peterx@redhat.com>
>Cc: <stable@vger.kernel.org>
>Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
>[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@google.com>

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