[PATCH] nommu: add page_align to mmap

[PATCH] nommu: add page_align to mmap

[Bob Liu]

Currently on nommu arch mmap(),mremap() and munmap() doesn't do page_align()
which is incorrect and not consist with mmu arch.
This patch fix it.

Signed-off-by: Bob Liu <lliubbo@gmail.com>
---
 mm/nommu.c |   24 ++++++++++++++----------
 1 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/mm/nommu.c b/mm/nommu.c
index c4c542c..3febfd9 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1133,7 +1133,7 @@ static int do_mmap_private(struct vm_area_struct *vma,
 			   unsigned long capabilities)
 {
 	struct page *pages;
-	unsigned long total, point, n, rlen;
+	unsigned long total, point, n;
 	void *base;
 	int ret, order;
 
@@ -1157,13 +1157,12 @@ static int do_mmap_private(struct vm_area_struct *vma,
 		 * make a private copy of the data and map that instead */
 	}
 
-	rlen = PAGE_ALIGN(len);
 
 	/* allocate some memory to hold the mapping
 	 * - note that this may not return a page-aligned address if the object
 	 *   we're allocating is smaller than a page
 	 */
-	order = get_order(rlen);
+	order = get_order(len);
 	kdebug("alloc order %d for %lx", order, len);
 
 	pages = alloc_pages(GFP_KERNEL, order);
@@ -1173,7 +1172,7 @@ static int do_mmap_private(struct vm_area_struct *vma,
 	total = 1 << order;
 	atomic_long_add(total, &mmap_pages_allocated);
 
-	point = rlen >> PAGE_SHIFT;
+	point = len >> PAGE_SHIFT;
 
 	/* we allocated a power-of-2 sized page set, so we may want to trim off
 	 * the excess */
@@ -1195,7 +1194,7 @@ static int do_mmap_private(struct vm_area_struct *vma,
 	base = page_address(pages);
 	region->vm_flags = vma->vm_flags |= VM_MAPPED_COPY;
 	region->vm_start = (unsigned long) base;
-	region->vm_end   = region->vm_start + rlen;
+	region->vm_end   = region->vm_start + len;
 	region->vm_top   = region->vm_start + (total << PAGE_SHIFT);
 
 	vma->vm_start = region->vm_start;
@@ -1211,15 +1210,15 @@ static int do_mmap_private(struct vm_area_struct *vma,
 
 		old_fs = get_fs();
 		set_fs(KERNEL_DS);
-		ret = vma->vm_file->f_op->read(vma->vm_file, base, rlen, &fpos);
+		ret = vma->vm_file->f_op->read(vma->vm_file, base, len, &fpos);
 		set_fs(old_fs);
 
 		if (ret < 0)
 			goto error_free;
 
 		/* clear the last little bit */
-		if (ret < rlen)
-			memset(base + ret, 0, rlen - ret);
+		if (ret < len)
+			memset(base + ret, 0, len - ret);
 
 	}
 
@@ -1268,6 +1267,7 @@ unsigned long do_mmap_pgoff(struct file *file,
 
 	/* we ignore the address hint */
 	addr = 0;
+	len = PAGE_ALIGN(len);
 
 	/* we've determined that we can make the mapping, now translate what we
 	 * now know into VMA flags */
@@ -1645,14 +1645,16 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len)
 {
 	struct vm_area_struct *vma;
 	struct rb_node *rb;
-	unsigned long end = start + len;
+	unsigned long end;
 	int ret;
 
 	kenter(",%lx,%zx", start, len);
 
-	if (len == 0)
+	if ((len = PAGE_ALIGN(len)) == 0)
 		return -EINVAL;
 
+	end = start + len;
+
 	/* find the first potentially overlapping VMA */
 	vma = find_vma(mm, start);
 	if (!vma) {
@@ -1773,6 +1775,8 @@ unsigned long do_mremap(unsigned long addr,
 	struct vm_area_struct *vma;
 
 	/* insanity checks first */
+	old_len = PAGE_ALIGN(old_len);
+	new_len = PAGE_ALIGN(new_len);
 	if (old_len == 0 || new_len == 0)
 		return (unsigned long) -EINVAL;
 
-- 
1.6.3.3


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Re: [PATCH] nommu: add page_align to mmap

[Andrew Morton]

On Wed, 27 Apr 2011 15:12:14 +0800
Bob Liu <lliubbo@gmail.com> wrote:

> Currently on nommu arch mmap(),mremap() and munmap() doesn't do page_align()
> which is incorrect and not consist with mmu arch.
> This patch fix it.
> 

Can you explain this fully please?  What was the user-observeable
behaviour before the patch, and after?

And some input from nommu maintainers would be nice.

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Re: [PATCH] nommu: add page_align to mmap

[Greg Ungerer]

On 05/05/11 07:13, Andrew Morton wrote:
> On Wed, 27 Apr 2011 15:12:14 +0800
> Bob Liu<lliubbo@gmail.com>  wrote:
>
>> Currently on nommu arch mmap(),mremap() and munmap() doesn't do page_align()
>> which is incorrect and not consist with mmu arch.
>> This patch fix it.
>>
>
> Can you explain this fully please?  What was the user-observeable
> behaviour before the patch, and after?
>
> And some input from nommu maintainers would be nice.

Its not obvious to me that there is a problem here. Are there
any issues caused by the current behavior that this fixes?

Regards
Greg


------------------------------------------------------------------------
Greg Ungerer  --  Principal Engineer        EMAIL:     gerg@snapgear.com
SnapGear Group, McAfee                      PHONE:       +61 7 3435 2888
8 Gardner Close                             FAX:         +61 7 3217 5323
Milton, QLD, 4064, Australia                WEB: http://www.SnapGear.com

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Re: [PATCH] nommu: add page_align to mmap

[Bob Liu]

On Thu, May 5, 2011 at 9:38 AM, Greg Ungerer <gerg@snapgear.com> wrote:
> On 05/05/11 07:13, Andrew Morton wrote:
>>
>> On Wed, 27 Apr 2011 15:12:14 +0800
>> Bob Liu<lliubbo@gmail.com>  wrote:
>>
>>> Currently on nommu arch mmap(),mremap() and munmap() doesn't do
>>> page_align()
>>> which is incorrect and not consist with mmu arch.
>>> This patch fix it.
>>>
>>
>> Can you explain this fully please?  What was the user-observeable
>> behaviour before the patch, and after?
>>
>> And some input from nommu maintainers would be nice.
>
> Its not obvious to me that there is a problem here. Are there
> any issues caused by the current behavior that this fixes?
>

Yes, there is a issue.

Some drivers'  mmap() function depend on (vma->vm_end - vma->start) is
page aligned which is true on mmu arch but not on nommu.
eg: uvc camera driver.

What's more, sometimes I got munmap() error.
The reason is split file: mm/nommu.c
                   do {
1614                         if (start > vma->vm_start) {
1615                                 kleave(" = -EINVAL [miss]");
1616                                 return -EINVAL;
1617                         }
1618                         if (end == vma->vm_end)
1619                                 goto erase_whole_vma;

<<=====================here
1620                         rb = rb_next(&vma->vm_rb);
1621                         vma = rb_entry(rb, struct vm_area_struct, vm_rb);
1622                 } while (rb);
1623                 kleave(" = -EINVAL [split file]");

Because end is not page aligned (passed into from userspace) while
some unknown reason
vma->vm_end is aligned,  this loop will fail and -EINVAL[split file]
error returned.
But it's hard to reproduce.

And in my opinion consist with mmu alway a better choice.

Thanks for your review.

-- 
Regards,
--Bob

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Re: [PATCH] nommu: add page_align to mmap

[Greg Ungerer]

Hi Bob,

On 05/05/11 20:19, Bob Liu wrote:
> On Thu, May 5, 2011 at 9:38 AM, Greg Ungerer<gerg@snapgear.com>  wrote:
>> On 05/05/11 07:13, Andrew Morton wrote:
>>>
>>> On Wed, 27 Apr 2011 15:12:14 +0800
>>> Bob Liu<lliubbo@gmail.com>  áwrote:
>>>
>>>> Currently on nommu arch mmap(),mremap() and munmap() doesn't do
>>>> page_align()
>>>> which is incorrect and not consist with mmu arch.
>>>> This patch fix it.
>>>>
>>>
>>> Can you explain this fully please? áWhat was the user-observeable
>>> behaviour before the patch, and after?
>>>
>>> And some input from nommu maintainers would be nice.
>>
>> Its not obvious to me that there is a problem here. Are there
>> any issues caused by the current behavior that this fixes?
>>
>
> Yes, there is a issue.
>
> Some drivers'  mmap() function depend on (vma->vm_end - vma->start) is
> page aligned which is true on mmu arch but not on nommu.
> eg: uvc camera driver.
>
> What's more, sometimes I got munmap() error.
> The reason is split file: mm/nommu.c
>                     do {
> 1614                         if (start>  vma->vm_start) {
> 1615                                 kleave(" = -EINVAL [miss]");
> 1616                                 return -EINVAL;
> 1617                         }
> 1618                         if (end == vma->vm_end)
> 1619                                 goto erase_whole_vma;
>
> <<=====================here
> 1620                         rb = rb_next(&vma->vm_rb);
> 1621                         vma = rb_entry(rb, struct vm_area_struct, vm_rb);
> 1622                 } while (rb);
> 1623                 kleave(" = -EINVAL [split file]");
>
> Because end is not page aligned (passed into from userspace) while
> some unknown reason
> vma->vm_end is aligned,  this loop will fail and -EINVAL[split file]
> error returned.
> But it's hard to reproduce.
>
> And in my opinion consist with mmu alway a better choice.
>
> Thanks for your review.

Ok, makes sense. Can you add some of this writeup to the patch
commit message?

Regards
Greg


------------------------------------------------------------------------
Greg Ungerer  --  Principal Engineer        EMAIL:     gerg@snapgear.com
SnapGear Group, McAfee                      PHONE:       +61 7 3435 2888
8 Gardner Close                             FAX:         +61 7 3217 5323
Milton, QLD, 4064, Australia                WEB: http://www.SnapGear.com

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