linux-kernel - Re: [RFC][PATCH 2/3] mm/page_poison.c: Enable PAGE

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Date:	Tue, 26 Jan 2016 14:39:26 +0800
From:	Jianyu Zhan <nasa4836@...il.com>
To:	Laura Abbott <labbott@...oraproject.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Michal Hocko <mhocko@...e.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	kernel-hardening@...ts.openwall.com,
	Kees Cook <keescook@...omium.org>
Subject: Re: [RFC][PATCH 2/3] mm/page_poison.c: Enable PAGE_POISONING as a
 separate option

On Tue, Jan 26, 2016 at 12:55 AM, Laura Abbott
<labbott@...oraproject.org> 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?!




Thanks,
Jianyu Zhan