linux-kernel - Re: [PATCH 2/3] devmem: handle partial kmem write/read

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Date:	Tue, 15 Sep 2009 17:03:54 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Greg KH <greg@...ah.com>, Andi Kleen <andi@...stfloor.org>,
	Christoph Lameter <clameter@....com>,
	Ingo Molnar <mingo@...e.hu>, Tejun Heo <tj@...nel.org>,
	Nick Piggin <npiggin@...e.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] devmem: handle partial kmem write/read

On Tue, Sep 15, 2009 at 05:01:30PM +0800, Wu Fengguang wrote:
> On Tue, Sep 15, 2009 at 10:38:11AM +0800, KAMEZAWA Hiroyuki wrote:
> > On Tue, 15 Sep 2009 10:18:53 +0800
> > Wu Fengguang <fengguang.wu@...el.com> wrote:
> > 
> > > Return early on partial read/write, which may happen in future.
> > > (eg. hit hwpoison pages)
> > > 
> > Hmm, please modify vread() as you did in vwrite() and
> > 
> > ==
> >                kbuf = (char *)__get_free_page(GFP_KERNEL);
> >                 if (!kbuf)
> >                         return -ENOMEM;
> > ==
> > Add __GFP_ZERO to kbuf allocation, and just ignore vread()'s return value.
> > Then, this will be much simpler.
> 
> Thanks, here is the updated patch, which
> - updates vread/vwrite prototype to return 0 (or error code in future).
> - do zero fill in the callers
> Comment updates are ignored for now.

This patch also makes it trivial to add your
is_vmalloc_or_module_addr() fixes, like this :)

---
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
---
 drivers/char/mem.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- linux-mm.orig/drivers/char/mem.c	2009-09-15 16:58:06.000000000 +0800
+++ linux-mm/drivers/char/mem.c	2009-09-15 16:58:12.000000000 +0800
@@ -446,6 +446,10 @@ static ssize_t read_kmem(struct file *fi
 			return -ENOMEM;
 		while (count > 0) {
 			sz = size_inside_page(p, count);
+			if (!is_vmalloc_or_module_addr((void*)p)) {
+				ret = -EFAULT;
+				break;
+			}
 			ret = vread(kbuf, (char *)p, sz);
 			if (ret)
 				break;
@@ -546,6 +550,10 @@ 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)) {
+				ret = -EFAULT;
+				break;
+			}
 			n = copy_from_user(kbuf, buf, sz);
 			if (n) {
 				if (wrote + virtr)
--
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