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SubjectRe: [PATCH 0/3] /proc/kmem cleanups and hwpoison bits
On Tue, 15 Sep 2009 10:18:51 +0800
Wu Fengguang <fengguang.wu@intel.com> wrote:

> Hi Kame,
>
> Here are 3 more kmem patches in my queue. Comments are welcome.
> If you feel good about them, I can send all recent kmem cleanup
> patches for you.
>

This is my quick hack. But I don't want to be an obstacle for you.
So, I'll wait for your updates.

==
Now, /dev/kmem's read/write vmalloc area doesn't do
range-check. Because vread/vwrite traverse vmalloc area list
under system-wide spinlock, it's better to avoid unnecessary
to do unnecessary calls to vread/vwrite.

And, vread/vwrite returns 0 if we accessed memory holes.
We can avoid copy-to-user in read side, we just ignore at write.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
drivers/char/mem.c | 27 +++++++++++++++++++--------
1 file changed, 19 insertions(+), 8 deletions(-)
Index: linux-2.6.31/drivers/char/mem.c
===================================================================
--- linux-2.6.31.orig/drivers/char/mem.c
+++ linux-2.6.31/drivers/char/mem.c
@@ -437,17 +437,19 @@ static ssize_t read_kmem(struct file *fi
}

if (count > 0) {
- kbuf = (char *)__get_free_page(GFP_KERNEL);
+ kbuf = (char *)__get_free_page(GFP_KERNEL | __GFP_ZERO);
if (!kbuf)
return -ENOMEM;
while (count > 0) {
sz = size_inside_page(p, count);
- sz = vread(kbuf, (char *)p, sz);
- if (!sz)
- break;
- if (copy_to_user(buf, kbuf, sz)) {
- free_page((unsigned long)kbuf);
- return -EFAULT;
+ if (is_vmalloc_or_module_addr((void*)p)) {
+ /* returns Non-zero if a page is found */
+ if (vread(kbuf, (char *)p, sz))
+ if (copy_to_user(buf, kbuf, sz)) {
+ free_page((unsigned long)kbuf);
+ return -EFAULT;
+ }
+ }
}
count -= sz;
buf += sz;
@@ -541,6 +543,11 @@ static ssize_t write_kmem(struct file *
unsigned long sz = size_inside_page(p, count);
unsigned long n;

+ if (is_vmalloc_or_module_addr((void*)p)) {
+ free_page((unsignedl long)kbuf);
+ retrun -EFAULT;
+ }
+
n = copy_from_user(kbuf, buf, sz);
if (n) {
if (wrote + virtr)
@@ -548,7 +555,11 @@ static ssize_t write_kmem(struct file *
free_page((unsigned long)kbuf);
return -EFAULT;
}
- sz = vwrite(kbuf, (char *)p, sz);
+ /*
+ * returns non-zero if copied successfully....
+ * But we don't care it. just make a progress.
+ */
+ vwrite(kbuf, (char *)p, sz);
count -= sz;
buf += sz;
virtr += sz;



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