Re: [PATCH RFC v3 25/36] kmsan: unpoison |tlb| in arch_tlb_gather_mmu()

[Andrey Konovalov <andreyknvl@google.com>]

On Fri, Nov 22, 2019 at 12:27 PM <glider@google.com> wrote:
>
> This is a hack to reduce stackdepot pressure.

I think this patch needs a better description :) Like in the comment below.

>
> Signed-off-by: Alexander Potapenko <glider@google.com>
> To: Alexander Potapenko <glider@google.com>
> Cc: Vegard Nossum <vegard.nossum@oracle.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: linux-mm@kvack.org
>
> ---
>
> Change-Id: I22a201e7e4f67ed74f8129072f12e5351b26103a
> ---
>  mm/mmu_gather.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
> index 7d70e5c78f97..8c5ea2d2e7d5 100644
> --- a/mm/mmu_gather.c
> +++ b/mm/mmu_gather.c
> @@ -1,6 +1,7 @@
>  #include <linux/gfp.h>
>  #include <linux/highmem.h>
>  #include <linux/kernel.h>
> +#include <linux/kmsan-checks.h>
>  #include <linux/mmdebug.h>
>  #include <linux/mm_types.h>
>  #include <linux/pagemap.h>
> @@ -206,6 +207,15 @@ void tlb_flush_mmu(struct mmu_gather *tlb)
>  void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
>                         unsigned long start, unsigned long end)
>  {
> +       /*
> +        * TODO(glider): struct mmu_gather contains 7 1-bit fields packed into a

Remove TODO?

> +        * 32-bit unsigned int value. The remaining 25 bits remain uninitialized
> +        * and are never used, but KMSAN updates the origin for them in
> +        * zap_pXX_range() in mm/memory.c, thus creating very long origin
> +        * chains. This is technically correct, but consumes too much memory.
> +        * Unpoisoning the whole structure will prevent creating such chains.
> +        */
> +       kmsan_unpoison_shadow(tlb, sizeof(*tlb));
>         tlb->mm = mm;
>
>         /* Is it from 0 to ~0? */
> --
> 2.24.0.432.g9d3f5f5b63-goog
>