Re: [PATCH v4 2/2] kfence: skip all GFP_ZONEMASK allocations

[Marco Elver <elver@google.com>]

On Mon, 5 Jul 2021 at 16:05, Marco Elver <elver@google.com> wrote:
> Andrew,
>
> This series is ready to be picked up.
>
> If possible, kindly consider including it in an upcoming batch of
> mainline fixes.
>
> Thank you!

It'd be good to get this sorted -- please take another look.

Many thanks,
-- Marco

> On Wed, 30 Jun 2021 at 17:02, Alexander Potapenko <glider@google.com> wrote:
> > Allocation requests outside ZONE_NORMAL (MOVABLE, HIGHMEM or DMA) cannot
> > be fulfilled by KFENCE, because KFENCE memory pool is located in a
> > zone different from the requested one.
> >
> > Because callers of kmem_cache_alloc() may actually rely on the
> > allocation to reside in the requested zone (e.g. memory allocations done
> > with __GFP_DMA must be DMAable), skip all allocations done with
> > GFP_ZONEMASK and/or respective SLAB flags (SLAB_CACHE_DMA and
> > SLAB_CACHE_DMA32).
> >
> > Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure")
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Dmitry Vyukov <dvyukov@google.com>
> > Cc: Marco Elver <elver@google.com>
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Cc: Souptick Joarder <jrdr.linux@gmail.com>
> > Cc: stable@vger.kernel.org # 5.12+
> > Signed-off-by: Alexander Potapenko <glider@google.com>
> > Reviewed-by: Marco Elver <elver@google.com>
> >
> > ---
> >
> > v2:
> >  - added parentheses around the GFP clause, as requested by Marco
> > v3:
> >  - ignore GFP_ZONEMASK, which also covers __GFP_HIGHMEM and __GFP_MOVABLE
> >  - move the flag check at the beginning of the function, as requested by
> >    Souptick Joarder
> > v4:
> >  - minor fixes to description and comment formatting
> > ---
> >  mm/kfence/core.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> > index 33bb20d91bf6a..1cbdb62e6d0fb 100644
> > --- a/mm/kfence/core.c
> > +++ b/mm/kfence/core.c
> > @@ -740,6 +740,15 @@ void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)
> >         if (size > PAGE_SIZE)
> >                 return NULL;
> >
> > +       /*
> > +        * Skip allocations from non-default zones, including DMA. We cannot
> > +        * guarantee that pages in the KFENCE pool will have the requested
> > +        * properties (e.g. reside in DMAable memory).
> > +        */
> > +       if ((flags & GFP_ZONEMASK) ||
> > +           (s->flags & (SLAB_CACHE_DMA | SLAB_CACHE_DMA32)))
> > +               return NULL;
> > +
> >         /*
> >          * allocation_gate only needs to become non-zero, so it doesn't make
> >          * sense to continue writing to it and pay the associated contention
> > --
> > 2.32.0.93.g670b81a890-goog
> >