Re: [RFC][PATCH 2/3] mm/page_poison.c: Enable PAGE_POISONING as a separate option

[Laura Abbott]

On 01/25/2016 10:39 PM, Jianyu Zhan wrote:
> On Tue, Jan 26, 2016 at 12:55 AM, Laura Abbott
> <labbott@xxxxxxxxxxxxxxxxx> wrote:
> > --- a/mm/debug-pagealloc.c
> > +++ b/mm/debug-pagealloc.c
> > @@ -8,11 +8,5 @@
> >
> >   void __kernel_map_pages(struct page *page, int numpages, int enable)
> >   {
> > -       if (!page_poisoning_enabled())
> > -               return;
> > -
> > -       if (enable)
> > -               unpoison_pages(page, numpages);
> > -       else
> > -               poison_pages(page, numpages);
> > +       kernel_poison_pages(page, numpages, enable);
> >   }
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 63358d9..c733421 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -1002,6 +1002,7 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
> >                                             PAGE_SIZE << order);
> >          }
> >          arch_free_page(page, order);
> > +       kernel_poison_pages(page, 1 << order, 0);
> >          kernel_map_pages(page, 1 << order, 0);
> >
> >          return true;
> > @@ -1396,6 +1397,7 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
> >          set_page_refcounted(page);
> >
> >          arch_alloc_page(page, order);
> > +       kernel_poison_pages(page, 1 << order, 1);
> >          kernel_map_pages(page, 1 << order, 1);
> >          kasan_alloc_pages(page, order);
>
> kernel_map_pages() will fall back to page poisoning scheme for
> !ARCH_SUPPORTS_DEBUG_PAGEALLOC.
>
> IIUC,  calling kernel_poison_pages() before kernel_map_pages() will be
> equivalent to call kernel_poison_pages()
> twice?!

Yes, you are absolutely right. In the !ARCH_SUPPORTS_DEBUG_PAGEALLOC
case we shouldn't need to do anything in kernel_map_pages.

> Thanks,
> Jianyu Zhan

Thanks,
Laura