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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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