* Re: + kcore-fix-vread-vwrite-to-be-aware-of-holes.patch added to -mm tree
[not found] <200908042130.n74LUxr8027929@imap1.linux-foundation.org>
@ 2009-08-05 7:38 ` KAMEZAWA Hiroyuki
2009-08-05 15:30 ` Américo Wang
0 siblings, 1 reply; 2+ messages in thread
From: KAMEZAWA Hiroyuki @ 2009-08-05 7:38 UTC (permalink / raw)
To: akpm; +Cc: nickpiggin, scgtrp, xiyou.wangcong, linux-kernel@vger.kernel.org
On Tue, 04 Aug 2009 14:30:58 -0700
akpm@linux-foundation.org wrote:
>
> The patch titled
> kcore: fix vread/vwrite to be aware of holes
> has been added to the -mm tree. Its filename is
> kcore-fix-vread-vwrite-to-be-aware-of-holes.patch
>
This is a replacement. Fixed comments where concerns are pointed out.
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.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_area() 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.) if IOREMAP is not set.
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.
Changelov v3->v3.1
- fixed comments. (mainly vread/vwrite description is updated.)
- use KM_USER0 instead of KM_USER1
Changelog v2->v3:
- fixed typos.
- added explaination of purge_lock.
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@jp.fujitsu.com>
---
mm/vmalloc.c | 199 ++++++++++++++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 176 insertions(+), 23 deletions(-)
Index: linux-2.6.31-rc5/mm/vmalloc.c
===================================================================
--- linux-2.6.31-rc5.orig/mm/vmalloc.c 2009-08-03 18:56:33.000000000 +0900
+++ linux-2.6.31-rc5/mm/vmalloc.c 2009-08-05 16:31:18.000000000 +0900
@@ -25,7 +25,7 @@
#include <linux/rcupdate.h>
#include <linux/pfn.h>
#include <linux/kmemleak.h>
-
+#include <linux/highmem.h>
#include <asm/atomic.h>
#include <asm/uaccess.h>
#include <asm/tlbflush.h>
@@ -1629,10 +1629,120 @@
}
EXPORT_SYMBOL(vmalloc_32_user);
+/*
+ * 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 = 0;
+
+ while (count) {
+ unsigned long offset, length;
+
+ offset = (unsigned long)addr & ~PAGE_MASK;
+ length = PAGE_SIZE - offset;
+ if (length > count)
+ length = count;
+ p = vmalloc_to_page(addr);
+ /*
+ * To do safe access to this _mapped_ area, we need
+ * lock. But adding lock here means that we need to add
+ * overhead of vmalloc()/vfree() calles for this _debug_
+ * interface, rarely used. Instead of that, we'll use
+ * kmap() and get small overhead in this access function.
+ */
+ if (p) {
+ /*
+ * we can expect USER0 is not used (see vread/vwrite's
+ * function description)
+ */
+ void *map = kmap_atomic(p, KM_USER0);
+ memcpy(buf, map + offset, length);
+ kunmap_atomic(map, KM_USER0);
+ } else
+ memset(buf, 0, length);
+
+ addr += length;
+ buf += length;
+ copied += length;
+ count -= length;
+ }
+ return copied;
+}
+
+static int aligned_vwrite(char *buf, char *addr, unsigned long count)
+{
+ struct page *p;
+ int copied = 0;
+
+ while (count) {
+ unsigned long offset, length;
+
+ offset = (unsigned long)addr & ~PAGE_MASK;
+ length = PAGE_SIZE - offset;
+ if (length > count)
+ length = count;
+ p = vmalloc_to_page(addr);
+ /*
+ * To do safe access to this _mapped_ area, we need
+ * lock. But adding lock here means that we need to add
+ * overhead of vmalloc()/vfree() calles for this _debug_
+ * interface, rarely used. Instead of that, we'll use
+ * kmap() and get small overhead in this access function.
+ */
+ if (p) {
+ /*
+ * we can expect USER0 is not used (see vread/vwrite's
+ * function description)
+ */
+ void *map = kmap_atomic(p, KM_USER0);
+ memcpy(map + offset, buf, length);
+ kunmap_atomic(map, KM_USER0);
+ }
+ addr += length;
+ buf += length;
+ copied += length;
+ count -= length;
+ }
+ return copied;
+}
+
+/**
+ * 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 number to @count). Returns 0 if [addr...addr+count) doesn't
+ * includes any intersect with alive vmalloc area.
+ *
+ * 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.
+ *
+ * If [addr...addr+count) doesn't includes any intersects with alive
+ * vm_struct area, returns 0.
+ * @buf should be kernel's buffer. Because this function uses KM_USER0,
+ * the caller should guarantee KM_USER0 is not used.
+ *
+ * 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.
+ *
+ */
+
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 +1750,7 @@
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 +1763,72 @@
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;
}
+/**
+ * vwrite() - write vmalloc area in a safe way.
+ * @buf: buffer for source data
+ * @addr: vm address.
+ * @count: number of bytes to be read.
+ *
+ * Returns # of bytes which addr and buf should be incresed.
+ * (same number to @count).
+ * If [addr...addr+count) doesn't includes any intersect with valid
+ * vmalloc area, returns 0.
+ *
+ * This function checks that addr is a valid vmalloc'ed area, and
+ * copy data from a buffer to the given addr. If specified range of
+ * [addr...addr+count) includes some valid address, data is copied from
+ * proper area of @buf. If there are memory holes, no copy to hole.
+ * IOREMAP area is treated as memory hole and no copy is done.
+ *
+ * If [addr...addr+count) doesn't includes any intersects with alive
+ * vm_struct area, returns 0.
+ * @buf should be kernel's buffer. Because this function uses KM_USER0,
+ * the caller should guarantee KM_USER0 is not used.
+ *
+ * Note: In usual ops, vwrite() 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 vwrite(char *buf, char *addr, unsigned long count)
{
struct vm_struct *tmp;
- char *vaddr, *buf_start = buf;
- unsigned long n;
+ char *vaddr;
+ unsigned long n, buflen;
+ int copied = 0;
/* Don't allow overflow */
if ((unsigned long) addr + count < count)
count = -(unsigned long) addr;
+ buflen = count;
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;
@@ -1690,18 +1840,21 @@
count--;
}
n = vaddr + tmp->size - PAGE_SIZE - addr;
- do {
- if (count == 0)
- goto finished;
- *addr = *buf;
- buf++;
- addr++;
- count--;
- } while (--n > 0);
+ if (n > count)
+ n = count;
+ if (!(tmp->flags & VM_IOREMAP)) {
+ aligned_vwrite(buf, addr, n);
+ copied++;
+ }
+ buf += n;
+ addr += n;
+ count -= n;
}
finished:
read_unlock(&vmlist_lock);
- return buf - buf_start;
+ if (!copied)
+ return 0;
+ return buflen;
}
/**
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