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Date: Tue, 4 Aug 2009 18:55:26 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: Amerigo Wang <xiyou.wangcong@...il.com>
Cc: Mike Smith <scgtrp@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
bugzilla-daemon@...zilla.kernel.org,
bugme-daemon@...zilla.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [BUGFIX][PATCH 2/3] kcore: fix vread/vwrite to be aware of
holes.
On Tue, 4 Aug 2009 17:23:16 +0800
Amerigo Wang <xiyou.wangcong@...il.com> wrote:
> On Mon, Aug 03, 2009 at 08:18:45PM +0900, KAMEZAWA Hiroyuki wrote:
> >From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> >
> >vread/vwrite access vmalloc area without checking there is a page or not.
> >In most case, this works well.
> >
> >In old ages, the caller of get_vm_ara() is only IOREMAP and there is no
> >memory hole within vm_struct's [addr...addr + size - PAGE_SIZE]
> >( -PAGE_SIZE is for a guard page.)
> >
> >After per-cpu-alloc patch, it uses get_vm_area() for reserve continuous
> >virtual address but remap _later_. There tend to be a hole in valid vmalloc
> >area in vm_struct lists.
> >Then, skip the hole (not mapped page) is necessary.
> >This patch updates vread/vwrite() for avoiding memory hole.
> >
> >Routines which access vmalloc area without knowing for which addr is used
> >are
> > - /proc/kcore
> > - /dev/kmem
> >
> >kcore checks IOREMAP, /dev/kmem doesn't. After this patch, IOREMAP is
> >checked and /dev/kmem will avoid to read/write it.
> >Fixes to /proc/kcore will be in the next patch in series.
> >
> >Changelog v2->v3:
> > - fixed typos.
> > - use kmap. (if not using kmap, we have to add lock here.)
>
>
> Hmm.. I missed this.
>
>
> > - fixed PAGE_MASK miss-use.
> >Changelog v1->v2:
> > - enhanced comments.
> > - treat IOREMAP as hole always.
> > - zero-fill memory hole if [addr...addr+size] includes valid pages.
> > - returns 0 if [addr...addr+size) includes no valid pages.
> >
> >Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>
>
> This time it looks much better now, but it still has a small problem.
> Please check it below.
>
>
thanks.
> >---
> > mm/vmalloc.c | 182 +++++++++++++++++++++++++++++++++++++++++++++++++++--------
> > 1 file changed, 159 insertions(+), 23 deletions(-)
> >
>
> <snip>
>
>
> >+
> >+/**
> >+ * vread() - read vmalloc area in a safe way.
> >+ * @buf: buffer for reading data
> >+ * @addr: vm address.
> >+ * @count: number of bytes to be read.
> >+ *
> >+ * Returns # of bytes which addr and buf should be increased.
> >+ * (same to count).
> >+ * If [addr...addr+count) doesn't includes any valid area, returns 0.
>
>
> If I read it correctly, your code doesn't do what you described here,
> it doesn't return 0 when there is no valid area.
>
Hmm.. valid area is ambiguous, ok, how about this ?
If [addr...addr+count) has no intersects with exisiting vm_struct, returns 0.
Thanks,
-Kame
>
> >+ *
> >+ * This function checks that addr is a valid vmalloc'ed area, and
> >+ * copy data from that area to a given buffer. If the given memory range of
> >+ * [addr...addr+count) includes some valid address, data is copied to
> >+ * proper area of @buf. If there are memory holes, they'll be zero-filled.
> >+ * IOREMAP area is treated as memory hole and no copy is done.
> >+ *
> >+ * Note: In usual ops, vread() is never necessary because the caller should
> >+ * know vmalloc() area is valid and can use memcpy(). This is for routines
> >+ * which have to access vmalloc area without any informaion, as /dev/kmem.
> >+ *
> >+ * The caller should guarantee KM_USER1 is not used.
> >+ */
> >+
> > long vread(char *buf, char *addr, unsigned long count)
> > {
> > struct vm_struct *tmp;
> > char *vaddr, *buf_start = buf;
> >+ unsigned long buflen = count;
> > unsigned long n;
> >
> > /* Don't allow overflow */
> >@@ -1640,7 +1739,7 @@
> > count = -(unsigned long) addr;
> >
> > read_lock(&vmlist_lock);
> >- for (tmp = vmlist; tmp; tmp = tmp->next) {
> >+ for (tmp = vmlist; count && tmp; tmp = tmp->next) {
> > vaddr = (char *) tmp->addr;
> > if (addr >= vaddr + tmp->size - PAGE_SIZE)
> > continue;
> >@@ -1653,32 +1752,66 @@
> > count--;
> > }
> > n = vaddr + tmp->size - PAGE_SIZE - addr;
> >- do {
> >- if (count == 0)
> >- goto finished;
> >- *buf = *addr;
> >- buf++;
> >- addr++;
> >- count--;
> >- } while (--n > 0);
> >+ if (n > count)
> >+ n = count;
> >+ if (!(tmp->flags & VM_IOREMAP))
> >+ aligned_vread(buf, addr, n);
> >+ else /* IOREMAP area is treated as memory hole */
> >+ memset(buf, 0, n);
> >+ buf += n;
> >+ addr += n;
> >+ count -= n;
> > }
> > finished:
> > read_unlock(&vmlist_lock);
> >- return buf - buf_start;
> >+
> >+ if (buf == buf_start)
> >+ return 0;
> >+ /* zero-fill memory holes */
> >+ if (buf != buf_start + buflen)
> >+ memset(buf, 0, buflen - (buf - buf_start));
> >+
> >+ return buflen;
> > }
>
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