On Thu, Dec 15, 2022 at 7:47 AM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On Mon, Dec 12, 2022 at 06:32:35PM +0100, Jann Horn wrote:
> > 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;
> > ugly hack needed in <=4.19 for s390]
> > Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
>
> All now queued up, thanks for the backports!
Uuugh, as reported by the kernel test robot, when you build this code
on 32-bit ARM with LPAE, it fails to build. The robot reported it for
4.14 but it also applies to 4.19. I'll go and fix this up again for
<=4.19...
