lkml.org 
[lkml]   [2012]   [Feb]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
Date
drm/i915 wants to read/write more than one page in its fastpath
and hence needs to prefault more than PAGE_SIZE bytes.

I've checked the callsites and they all already clamp size when
calling fault_in_pages_* to the same as for the subsequent
__copy_to|from_user and hence don't rely on the implicit clamping
to PAGE_SIZE.
Also kill a copy&pasted spurious space in both functions while at it.

v2: As suggested by Andrew Morton, add a multipage parameter to both
functions to avoid the additional branch for the pagemap.c hotpath.
My gcc 4.6 here seems to dtrt and indeed reap these branches where not
needed.

Cc: linux-mm@kvack.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
drivers/gpu/drm/i915/i915_gem.c | 4 +-
drivers/gpu/drm/i915/i915_gem_execbuffer.c | 2 +-
fs/pipe.c | 4 +-
fs/splice.c | 2 +-
include/linux/pagemap.h | 39 ++++++++++++++++++---------
mm/filemap.c | 4 +-
6 files changed, 34 insertions(+), 21 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 544e528..9b200f4e 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -436,7 +436,7 @@ i915_gem_shmem_pread(struct drm_device *dev,
mutex_unlock(&dev->struct_mutex);

if (!prefaulted) {
- ret = fault_in_pages_writeable(user_data, remain);
+ ret = fault_in_pages_writeable(user_data, remain, true);
/* Userspace is tricking us, but we've already clobbered
* its pages with the prefault and promised to write the
* data up to the first fault. Hence ignore any errors
@@ -823,7 +823,7 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
return -EFAULT;

ret = fault_in_pages_readable((char __user *)(uintptr_t)args->data_ptr,
- args->size);
+ args->size, true);
if (ret)
return -EFAULT;

diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 81687af..5f0b685 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -955,7 +955,7 @@ validate_exec_list(struct drm_i915_gem_exec_object2 *exec,
if (!access_ok(VERIFY_WRITE, ptr, length))
return -EFAULT;

- if (fault_in_pages_readable(ptr, length))
+ if (fault_in_pages_readable(ptr, length, true))
return -EFAULT;
}

diff --git a/fs/pipe.c b/fs/pipe.c
index a932ced..b29f71c 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -167,7 +167,7 @@ static int iov_fault_in_pages_write(struct iovec *iov, unsigned long len)
unsigned long this_len;

this_len = min_t(unsigned long, len, iov->iov_len);
- if (fault_in_pages_writeable(iov->iov_base, this_len))
+ if (fault_in_pages_writeable(iov->iov_base, this_len, false))
break;

len -= this_len;
@@ -189,7 +189,7 @@ static void iov_fault_in_pages_read(struct iovec *iov, unsigned long len)
unsigned long this_len;

this_len = min_t(unsigned long, len, iov->iov_len);
- fault_in_pages_readable(iov->iov_base, this_len);
+ fault_in_pages_readable(iov->iov_base, this_len, false);
len -= this_len;
iov++;
}
diff --git a/fs/splice.c b/fs/splice.c
index 1ec0493..e919d78 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1491,7 +1491,7 @@ static int pipe_to_user(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
* See if we can use the atomic maps, by prefaulting in the
* pages and doing an atomic copy
*/
- if (!fault_in_pages_writeable(sd->u.userptr, sd->len)) {
+ if (!fault_in_pages_writeable(sd->u.userptr, sd->len, false)) {
src = buf->ops->map(pipe, buf, 1);
ret = __copy_to_user_inatomic(sd->u.userptr, src + buf->offset,
sd->len);
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index cfaaa69..60ac5c5 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -403,11 +403,14 @@ extern void add_page_wait_queue(struct page *page, wait_queue_t *waiter);
* Fault a userspace page into pagetables. Return non-zero on a fault.
*
* This assumes that two userspace pages are always sufficient. That's
- * not true if PAGE_CACHE_SIZE > PAGE_SIZE.
+ * not true if PAGE_CACHE_SIZE > PAGE_SIZE. If more than PAGE_SIZE needs to be
+ * prefaulted, set multipage to true.
*/
-static inline int fault_in_pages_writeable(char __user *uaddr, int size)
+static inline int fault_in_pages_writeable(char __user *uaddr, int size,
+ bool multipage)
{
int ret;
+ char __user *end = uaddr + size - 1;

if (unlikely(size == 0))
return 0;
@@ -416,36 +419,46 @@ static inline int fault_in_pages_writeable(char __user *uaddr, int size)
* Writing zeroes into userspace here is OK, because we know that if
* the zero gets there, we'll be overwriting it.
*/
- ret = __put_user(0, uaddr);
- if (ret == 0) {
- char __user *end = uaddr + size - 1;
+ do {
+ ret = __put_user(0, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ } while (multipage && uaddr <= end);

+ if (ret == 0) {
/*
* If the page was already mapped, this will get a cache miss
* for sure, so try to avoid doing it.
*/
- if (((unsigned long)uaddr & PAGE_MASK) !=
+ if (((unsigned long)uaddr & PAGE_MASK) ==
((unsigned long)end & PAGE_MASK))
- ret = __put_user(0, end);
+ ret = __put_user(0, end);
}
return ret;
}

-static inline int fault_in_pages_readable(const char __user *uaddr, int size)
+static inline int fault_in_pages_readable(const char __user *uaddr, int size,
+ bool multipage)
{
volatile char c;
int ret;
+ const char __user *end = uaddr + size - 1;

if (unlikely(size == 0))
return 0;

- ret = __get_user(c, uaddr);
- if (ret == 0) {
- const char __user *end = uaddr + size - 1;
+ do {
+ ret = __get_user(c, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ } while (multipage && uaddr <= end);

- if (((unsigned long)uaddr & PAGE_MASK) !=
+ if (ret == 0) {
+ if (((unsigned long)uaddr & PAGE_MASK) ==
((unsigned long)end & PAGE_MASK)) {
- ret = __get_user(c, end);
+ ret = __get_user(c, end);
(void)c;
}
}
diff --git a/mm/filemap.c b/mm/filemap.c
index 97f49ed..af2cad5 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1317,7 +1317,7 @@ int file_read_actor(read_descriptor_t *desc, struct page *page,
* Faults on the destination of a read are common, so do it before
* taking the kmap.
*/
- if (!fault_in_pages_writeable(desc->arg.buf, size)) {
+ if (!fault_in_pages_writeable(desc->arg.buf, size, false)) {
kaddr = kmap_atomic(page, KM_USER0);
left = __copy_to_user_inatomic(desc->arg.buf,
kaddr + offset, size);
@@ -2138,7 +2138,7 @@ int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes)
{
char __user *buf = i->iov->iov_base + i->iov_offset;
bytes = min(bytes, i->iov->iov_len - i->iov_offset);
- return fault_in_pages_readable(buf, bytes);
+ return fault_in_pages_readable(buf, bytes, false);
}
EXPORT_SYMBOL(iov_iter_fault_in_readable);

--
1.7.7.5


\
 
 \ /
  Last update: 2012-02-29 15:09    [W:0.320 / U:0.244 seconds]
©2003-2014 Jasper Spaans. Advertise on this site