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Commit f56f821f authored by Daniel Vetter's avatar Daniel Vetter
Browse files

mm: extend prefault helpers to fault in more than PAGE_SIZE 



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.

v4: Adjust comment to CodingStlye and fix spelling.

Acked-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
parent d174bd64

drivers/gpu/drm/i915/i915_gem.c

+3 −3
Original line number Diff line number Diff line
@@ -416,7 +416,7 @@ 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
@@ -809,7 +809,7 @@ 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,

	ret = fault_in_multipages_readable((char __user *)(uintptr_t)args->data_ptr,

					   args->size);

	if (ret)

		return -EFAULT;

drivers/gpu/drm/i915/i915_gem_execbuffer.c

+1 −1
Original line number Diff line number Diff line
@@ -997,7 +997,7 @@ 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;

	}

include/linux/pagemap.h

+62 −2
Original line number Diff line number Diff line
@@ -452,6 +452,66 @@ static inline int fault_in_pages_readable(const char __user *uaddr, int size) 
	return ret;

}



/*

 * Multipage variants of the above prefault helpers, useful if more than

 * PAGE_SIZE of data 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,