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Date: Wed, 29 Jul 2009 17:59:32 +0800
From: Amerigo Wang <xiyou.wangcong@...il.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: Mike Smith <scgtrp@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
bugzilla-daemon@...zilla.kernel.org,
bugme-daemon@...zilla.kernel.org,
Amerigo Wang <xiyou.wangcong@...il.com>,
linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 2/2] vmalloc: vread vwrite avoid memory hole.
On Wed, Jul 29, 2009 at 05:48:10PM +0900, KAMEZAWA Hiroyuki wrote:
>Considering recent changes, I think this an answer to this bug.
>
>All get_vm_area() calls specified VM_IOREMAP before 2.6.30.
>Now, percpu calls get_vm_area() without IOREMAP (it means kcore doesn't skip this)
>And it seems pcpu does delayed map to pre-allocated vmalloc-area.
>Then, now, vmalloc() area has memory holes. (I'm sorry if I misunderstand.)
You mean the guard holes in vmalloc area?
IIRC, there are some guard holes between vmalloc areas, but I haven't
checked the source code. ;)
>Then, vread()/vwrite() should be aware of memory holes in vmalloc.
>And yes, /proc/kcore should be.
>
>plz review.
>==
>vread/vwrite access vmalloc area without checking there is a page or not.
>In most case, this works well.
>
>After per-cpu-alloc patch, There tend to be a hole in valid vmalloc area.
>Then, skip the hole (not mapped page) is necessary.
>
>/proc/kcore has the same problem, now, it uses its own code but
>it's better to use vread().
>
>Question: vread() should skip IOREMAP area always ?
>
>Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Some comments below..
>---
> drivers/char/mem.c | 3 +
> fs/proc/kcore.c | 32 +----------------
> include/linux/vmalloc.h | 3 +
> mm/vmalloc.c | 90 +++++++++++++++++++++++++++++++++++++-----------
> 4 files changed, 77 insertions(+), 51 deletions(-)
>
>Index: linux-2.6.31-rc4/mm/vmalloc.c
>===================================================================
>--- linux-2.6.31-rc4.orig/mm/vmalloc.c
>+++ linux-2.6.31-rc4/mm/vmalloc.c
>@@ -1629,7 +1629,61 @@ void *vmalloc_32_user(unsigned long size
> }
> EXPORT_SYMBOL(vmalloc_32_user);
>
>-long vread(char *buf, char *addr, unsigned long count)
>+/*
>+ * small helper routine , copy contents to buf from addr.
>+ * If the page is not present, fill zero.
>+ */
>+
>+static int aligned_vread(char *buf, char *addr, unsigned long count)
>+{
>+ struct page *p;
>+ int copied;
>+
>+ while (count) {
>+ unsigned long offset, length;
>+
>+ offset = (unsinged long)addr & PAGE_MASK;
>+ length = PAGE_SIZE - offset;
>+ if (length > count)
>+ length = count;
>+ p = vmalloc_to_page(addr);
>+ if (p)
>+ memcpy(buf, addr, length);
>+ else
>+ memset(buf, 0, length);
>+ addr += length;
>+ buf += length;
>+ copiled += length;
>+ count -= length;
>+ }
>+ return copied;
>+}
>+
>+static int aligned_vwrite(char *buf, char *addr, unsigned long count)
>+{
>+ struct page *p;
>+ int copied;
>+
>+ while (count) {
>+ unsigned long offset, length;
>+
>+ offset = (unsinged long)addr & PAGE_MASK;
>+ length = PAGE_SIZE - offset;
>+ if (length > count)
>+ length = count;
>+ /* confirm the page is present */
>+ p = vmalloc_to_page(addr);
>+ if (p)
>+ memcpy(addr, buf, length);
So when !p, you copy nothing, but still increase the length,
*silently*?
This looks a bit weird for me... I am thinking if we need
to return the number of bytes that is *actually* copied?
>+ addr += length;
>+ buf += length;
>+ copiled += length;
>+ count -= length;
>+ }
>+ return copied;
>+}
>+
>+long vread(char *buf, char *addr, unsigned long count, bool skip_ioremap)
> {
> struct vm_struct *tmp;
> char *vaddr, *buf_start = buf;
>@@ -1640,10 +1694,11 @@ long vread(char *buf, char *addr, unsign
> 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;
>+
> while (addr < vaddr) {
> if (count == 0)
> goto finished;
>@@ -1653,14 +1708,15 @@ long vread(char *buf, char *addr, unsign
> 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) || !skip_ioremap)
>+ aligned_vread(buf, addr, n);
>+ else
>+ memset(buf, 0, n);
>+ buf += n;
>+ addr += n;
>+ count -= n;
If I set 'skip_ioremap' true, I want the return value can be
what it _actually_ copies, i.e. kick out the bytes counted
for VM_IOREMAP. What do you think?
> }
> finished:
> read_unlock(&vmlist_lock);
>@@ -1678,7 +1734,7 @@ long vwrite(char *buf, char *addr, unsig
> 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;
>@@ -1690,14 +1746,10 @@ long vwrite(char *buf, char *addr, unsig
> count--;
> }
> n = vaddr + tmp->size - PAGE_SIZE - addr;
>- do {
>- if (count == 0)
>- goto finished;
>- *addr = *buf;
>- buf++;
>- addr++;
>- count--;
>- } while (--n > 0);
>+ copied = aligned_vwrite(buf, addr, n);
>+ buf += n;
>+ addr += n;
>+ count -= n;
> }
> finished:
> read_unlock(&vmlist_lock);
>Index: linux-2.6.31-rc4/drivers/char/mem.c
>===================================================================
>--- linux-2.6.31-rc4.orig/drivers/char/mem.c
>+++ linux-2.6.31-rc4/drivers/char/mem.c
>@@ -466,7 +466,8 @@ static ssize_t read_kmem(struct file *fi
>
> if (len > PAGE_SIZE)
> len = PAGE_SIZE;
>- len = vread(kbuf, (char *)p, len);
>+ /* we read memory even if ioremap...*/
>+ len = vread(kbuf, (char *)p, len, false);
> if (!len)
> break;
> if (copy_to_user(buf, kbuf, len)) {
>Index: linux-2.6.31-rc4/fs/proc/kcore.c
>===================================================================
>--- linux-2.6.31-rc4.orig/fs/proc/kcore.c
>+++ linux-2.6.31-rc4/fs/proc/kcore.c
>@@ -331,40 +331,12 @@ read_kcore(struct file *file, char __use
> struct vm_struct *m;
> unsigned long curstart = start;
> unsigned long cursize = tsz;
>-
>+
I am sure this change, a line only has spaces, is not what you want. :-)
> elf_buf = kzalloc(tsz, GFP_KERNEL);
> if (!elf_buf)
> return -ENOMEM;
>
>- read_lock(&vmlist_lock);
>- for (m=vmlist; m && cursize; m=m->next) {
>- unsigned long vmstart;
>- unsigned long vmsize;
>- unsigned long msize = m->size - PAGE_SIZE;
>-
>- if (((unsigned long)m->addr + msize) <
>- curstart)
>- continue;
>- if ((unsigned long)m->addr > (curstart +
>- cursize))
>- break;
>- vmstart = (curstart < (unsigned long)m->addr ?
>- (unsigned long)m->addr : curstart);
>- if (((unsigned long)m->addr + msize) >
>- (curstart + cursize))
>- vmsize = curstart + cursize - vmstart;
>- else
>- vmsize = (unsigned long)m->addr +
>- msize - vmstart;
>- curstart = vmstart + vmsize;
>- cursize -= vmsize;
>- /* don't dump ioremap'd stuff! (TA) */
>- if (m->flags & VM_IOREMAP)
>- continue;
>- memcpy(elf_buf + (vmstart - start),
>- (char *)vmstart, vmsize);
>- }
>- read_unlock(&vmlist_lock);
>+ vread(elf_buf, start, tsz, true);
> if (copy_to_user(buffer, elf_buf, tsz)) {
> kfree(elf_buf);
> return -EFAULT;
>Index: linux-2.6.31-rc4/include/linux/vmalloc.h
>===================================================================
>--- linux-2.6.31-rc4.orig/include/linux/vmalloc.h
>+++ linux-2.6.31-rc4/include/linux/vmalloc.h
>@@ -105,7 +105,8 @@ extern struct vm_struct *alloc_vm_area(s
> extern void free_vm_area(struct vm_struct *area);
>
> /* for /dev/kmem */
>-extern long vread(char *buf, char *addr, unsigned long count);
>+extern long vread(char *buf, char *addr, unsigned long count,
>+ bool skip_ioremap);
> extern long vwrite(char *buf, char *addr, unsigned long count);
>
> /*
>
--
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