linux-kernel - Re: [PATCH 1/1] mm/hugetlb: Set PTE as huge in hugetlb_change

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Date:	Mon, 21 Jan 2013 11:04:10 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Tony Lu <zlu@...era.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Hillf Danton <dhillf@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Chris Metcalf <cmetcalf@...era.com>
Subject: Re: [PATCH 1/1] mm/hugetlb: Set PTE as huge in
 hugetlb_change_protection

On Mon 21-01-13 04:13:07, Tony Lu wrote:
> From da8432aafd231e7cdcda9d15484829def4663cb0 Mon Sep 17 00:00:00 2001
> From: Zhigang Lu <zlu@...era.com>
> Date: Mon, 21 Jan 2013 11:23:26 +0800
> Subject: [PATCH 1/1] mm/hugetlb: Set PTE as huge in hugetlb_change_protection
> 
> When setting a huge PTE, besides calling pte_mkhuge(), we also need
> to call arch_make_huge_pte(), which we indeed do in make_huge_pte(),
> but we forget to do in hugetlb_change_protection().

I guess you also need it in remove_migration_pte. This calls for a
helper which would do both pte_mkhuge() and arch_make_huge_pte.

Besides that, tile seem to be the only arch which implements this arch
hook (introduced by 621b1955 in 3.5) so this should be considered for
stable.

> 
> Signed-off-by: Zhigang Lu <zlu@...era.com>
> Signed-off-by: Chris Metcalf <cmetcalf@...era.com>
> ---
>  mm/hugetlb.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 4f3ea0b..546db81 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -3033,6 +3033,7 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
>                 if (!huge_pte_none(huge_ptep_get(ptep))) {
>                         pte = huge_ptep_get_and_clear(mm, address, ptep);
>                         pte = pte_mkhuge(pte_modify(pte, newprot));
> +                       pte = arch_make_huge_pte(pte, vma, NULL, 0);
>                         set_huge_pte_at(mm, address, ptep, pte);
>                         pages++;
>                 }
> -- 
> 1.7.10.3

-- 
Michal Hocko
SUSE Labs
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