Re: [PATCH] Fix virtual address handling in hugetlb fault

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 21 Nov 2011 19:48:32 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> >From 7c29389be2890c6b6934a80b4841d07a7014fe26 Mon Sep 17 00:00:00 2001
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Date: Mon, 21 Nov 2011 19:45:27 +0900
> Subject: [PATCH] Fix virtual address handling in hugetlb fault
> 
> handle_mm_fault() passes 'faulted' address to hugetlb_fault().
> Then, the address is not aligned to hugepage boundary.
> 
> Most of functions for hugetlb pages are aware of that and
> calculate an alignment by itself. Some functions as copy_user_huge_page(),
> and clear_huge_page() doesn't handle alignment by themselves.
> 
> This patch make hugeltb_fault() to calculate the alignment and pass
> aligned addresss (top address of a faulted hugepage) to functions.
> 

Does this actually fix any known user-visible misbehaviour?

It sounds like the code is masking addresses in a lot of different
places.  It would be better to do it once, at the top level.  Perhaps
this patch makes some of the existing masking obsolete?

> index bb28a5f..af37337 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2629,6 +2629,8 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
>  	static DEFINE_MUTEX(hugetlb_instantiation_mutex);
>  	struct hstate *h = hstate_vma(vma);
>  
> +	address = address & huge_page_mask(h);

--- a/mm/hugetlb.c~mm-hugetlbc-fix-virtual-address-handling-in-hugetlb-fault-fix
+++ a/mm/hugetlb.c
@@ -2639,7 +2639,7 @@ int hugetlb_fault(struct mm_struct *mm, 
 	static DEFINE_MUTEX(hugetlb_instantiation_mutex);
 	struct hstate *h = hstate_vma(vma);
 
-	address = address & huge_page_mask(h);
+	address &= huge_page_mask(h);
 
 	ptep = huge_pte_offset(mm, address);
 	if (ptep) {

is a bit more readable, IMO.

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