Re: [PATCH v3 stable 4.9,4.14 1/2] mm/khugepaged: fix GUP-fast interaction by sending IPI

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Jan 03, 2023 at 06:16:36PM +0100, Jann Horn wrote:
> On Tue, Jan 3, 2023 at 6:14 PM Jann Horn <jannh@google.com> 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@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;
> > ugly hack for s390 and arm in <=4.19]
> 
> Or if you just want a fixup commit, you can add this to 4.9, 4.14 and 4.19:
> 
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 0f217bb9b534..0a4cace1cfc4 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -24,7 +24,7 @@
>  #include "internal.h"
> 
>  /* gross hack for <=4.19 stable */
> -#ifdef CONFIG_S390
> +#if defined(CONFIG_S390) || defined(CONFIG_ARM)
>  static void tlb_remove_table_smp_sync(void *arg)
>  {
>          /* Simply deliver the interrupt */
> 
> Let me know if you want me to send a fixup instead, since the
> broken-on-arm version of this patch is already in a stable RC...

This works, now all fixed up in all 3 queues, thanks!

greg k-h