linux-kernel - Re: [PATCH v8 5/9] vmalloc: introduce remap_vmalloc_range

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Message-Id: <20130523150035.73dc8457e895155897ef8781@linux-foundation.org>
Date:	Thu, 23 May 2013 15:00:35 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
Cc:	vgoyal@...hat.com, ebiederm@...ssion.com, cpw@....com,
	kumagai-atsushi@....nes.nec.co.jp, lisa.mitchell@...com,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	zhangyanfei@...fujitsu.com, jingbai.ma@...com, linux-mm@...ck.org,
	riel@...hat.com, walken@...gle.com, hughd@...gle.com,
	kosaki.motohiro@...fujitsu.com
Subject: Re: [PATCH v8 5/9] vmalloc: introduce remap_vmalloc_range_partial

On Thu, 23 May 2013 14:25:24 +0900 HATAYAMA Daisuke <d.hatayama@...fujitsu.com> wrote:

> We want to allocate ELF note segment buffer on the 2nd kernel in
> vmalloc space and remap it to user-space in order to reduce the risk
> that memory allocation fails on system with huge number of CPUs and so
> with huge ELF note segment that exceeds 11-order block size.
> 
> Although there's already remap_vmalloc_range for the purpose of
> remapping vmalloc memory to user-space, we need to specify user-space
> range via vma. Mmap on /proc/vmcore needs to remap range across
> multiple objects, so the interface that requires vma to cover full
> range is problematic.
> 
> This patch introduces remap_vmalloc_range_partial that receives
> user-space range as a pair of base address and size and can be used
> for mmap on /proc/vmcore case.
> 
> remap_vmalloc_range is rewritten using remap_vmalloc_range_partial.
> 
> ...
>
> +int remap_vmalloc_range_partial(struct vm_area_struct *vma, unsigned long uaddr,
> +				void *kaddr, unsigned long size)
>  {
>  	struct vm_struct *area;
> -	unsigned long uaddr = vma->vm_start;
> -	unsigned long usize = vma->vm_end - vma->vm_start;
>  
> -	if ((PAGE_SIZE-1) & (unsigned long)addr)
> +	size = PAGE_ALIGN(size);
> +
> +	if (((PAGE_SIZE-1) & (unsigned long)uaddr) ||
> +	    ((PAGE_SIZE-1) & (unsigned long)kaddr))
>  		return -EINVAL;

hm, that's ugly.


Why don't we do this:

From: Andrew Morton <akpm@...ux-foundation.org>
Subject: include/linux/mm.h: add PAGE_ALIGNED() helper

To test whether an address is aligned to PAGE_SIZE.

Cc: HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>, 
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 include/linux/mm.h |    3 +++
 1 file changed, 3 insertions(+)

diff -puN include/linux/mm.h~a include/linux/mm.h
--- a/include/linux/mm.h~a
+++ a/include/linux/mm.h
@@ -52,6 +52,9 @@ extern unsigned long sysctl_admin_reserv
 /* to align the pointer to the (next) page boundary */
 #define PAGE_ALIGN(addr) ALIGN(addr, PAGE_SIZE)
 
+/* test whether an address (unsigned long or pointer) is aligned to PAGE_SIZE */
+#define PAGE_ALIGNED(addr)	IS_ALIGNED((unsigned long)addr, PAGE_SIZE)
+
 /*
  * Linux kernel virtual memory manager primitives.
  * The idea being to have a "virtual" mm in the same way
_


(I'd have thought we already had such a thing, but we don't seem to)


Then this:

From: Andrew Morton <akpm@...ux-foundation.org>
Subject: vmalloc-introduce-remap_vmalloc_range_partial-fix

use PAGE_ALIGNED()

Cc: Atsushi Kumagai <kumagai-atsushi@....nes.nec.co.jp>
Cc: HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: Lisa Mitchell <lisa.mitchell@...com>
Cc: Vivek Goyal <vgoyal@...hat.com>
Cc: Zhang Yanfei <zhangyanfei@...fujitsu.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 mm/vmalloc.c |    8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff -puN include/linux/vmalloc.h~vmalloc-introduce-remap_vmalloc_range_partial-fix include/linux/vmalloc.h
diff -puN mm/vmalloc.c~vmalloc-introduce-remap_vmalloc_range_partial-fix mm/vmalloc.c
--- a/mm/vmalloc.c~vmalloc-introduce-remap_vmalloc_range_partial-fix
+++ a/mm/vmalloc.c
@@ -1476,10 +1476,9 @@ static void __vunmap(const void *addr, i
 	if (!addr)
 		return;
 
-	if ((PAGE_SIZE-1) & (unsigned long)addr) {
-		WARN(1, KERN_ERR "Trying to vfree() bad address (%p)\n", addr);
+	if (WARN(!PAGE_ALIGNED(addr), "Trying to vfree() bad address (%p)\n",
+			addr));
 		return;
-	}
 
 	area = remove_vm_area(addr);
 	if (unlikely(!area)) {
@@ -2170,8 +2169,7 @@ int remap_vmalloc_range_partial(struct v
 
 	size = PAGE_ALIGN(size);
 
-	if (((PAGE_SIZE-1) & (unsigned long)uaddr) ||
-	    ((PAGE_SIZE-1) & (unsigned long)kaddr))
+	if (!PAGE_ALIGNED(uaddr) || !PAGE_ALIGNED(kaddr))
 		return -EINVAL;
 
 	area = find_vm_area(kaddr);
_

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