drm/i915 wants to read/write more than one page in its fastpath
and hence needs to prefault more than PAGE_SIZE bytes.
Add new functions in filemap.h to make that possible.
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.
v3: Becaus I couldn't find a way around adding a uaddr += PAGE_SIZE to
the filemap.c hotpaths (that the compiler couldn't remove again),
let's go with separate new functions for the multipage use-case.
Cc: linux-mm at kvack.org
Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
drivers/gpu/drm/i915/i915_gem.c | 6 +-
drivers/gpu/drm/i915/i915_gem_execbuffer.c | 2 +-
include/linux/pagemap.h | 62 +++++++++++++++++++++++++++-
3 files changed, 64 insertions(+), 6 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 544e528..3e631fc 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_multipages_writeable(user_data, remain);
/* 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
@@ -822,8 +822,8 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
args->size))
return -EFAULT;
- ret = fault_in_pages_readable((char __user *)(uintptr_t)args->data_ptr,
- args->size);
+ ret = fault_in_multipages_readable((char __user
*)(uintptr_t)args->data_ptr,
+ args->size);
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..ef87f52 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_multipages_readable(ptr, length))
return -EFAULT;
}
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index cfaaa69..0a91375 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -426,7 +426,7 @@ static inline int fault_in_pages_writeable(char __user
*uaddr, int size)
*/
if (((unsigned long)uaddr & PAGE_MASK) !=
((unsigned long)end & PAGE_MASK))
- ret = __put_user(0, end);
+ ret = __put_user(0, end);
}
return ret;
}
@@ -445,13 +445,71 @@ static inline int fault_in_pages_readable(const char
__user *uaddr, int size)
if (((unsigned long)uaddr & PAGE_MASK) !=
((unsigned long)end & PAGE_MASK)) {
- ret = __get_user(c, end);
+ ret = __get_user(c, end);
(void)c;
}
}
return ret;
}
+/* Multipage variants of the above prefault helpers, useful if more than
+ * PAGE_SIZE of date needs to be prefaulted. These are separate from the above
+ * functions (which only handle up to PAGE_SIZE) to avoid clobbering the
+ * filemap.c hotpaths. */
+static inline int fault_in_multipages_writeable(char __user *uaddr, int size)
+{
+ int ret;
+ const char __user *end = uaddr + size - 1;
+
+ if (unlikely(size == 0))
+ return 0;
+
+ /*
+ * Writing zeroes into userspace here is OK, because we know that if
+ * the zero gets there, we'll be overwriting it.
+ */
+ while (uaddr <= end) {
+ ret = __put_user(0, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ }
+
+ /* Check whether the range spilled into the next page. */
+ if (((unsigned long)uaddr & PAGE_MASK) ==
+ ((unsigned long)end & PAGE_MASK))
+ ret = __put_user(0, end);
+
+ return ret;
+}
+
+static inline int fault_in_multipages_readable(const char __user *uaddr,
+ int size)
+{
+ volatile char c;
+ int ret;
+ const char __user *end = uaddr + size - 1;
+
+ if (unlikely(size == 0))
+ return 0;
+
+ while (uaddr <= end) {
+ ret = __get_user(c, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ }
+
+ /* Check whether the range spilled into the next page. */
+ if (((unsigned long)uaddr & PAGE_MASK) ==
+ ((unsigned long)end & PAGE_MASK)) {
+ ret = __get_user(c, end);
+ (void)c;
+ }
+
+ return ret;
+}
+
int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
pgoff_t index, gfp_t gfp_mask);
int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
--
1.7.7.6
