[PATCH 67/76] drm/i915/userptr: Probe existence of backing struct pages upon creation

[Chris Wilson]

Jason Ekstrand requested a more efficient method than userptr+set-domain
to determine if the userptr object was backed by a complete set of pages
upon creation. To be more efficient than simply populating the userptr
using get_user_pages() (as done by the call to set-domain or execbuf),
we can walk the tree of vm_area_struct and check for gaps or vma not
backed by struct page (VM_PFNMAP). The question is how to handle
VM_MIXEDMAP which may be either struct page or pfn backed...

Testcase: igt/gem_userptr_blits/probe
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Michał Winiarski <michal.winiarski at intel.com>
Cc: Jason Ekstrand <jason at jlekstrand.net>
---
 drivers/gpu/drm/i915/i915_gem_userptr.c | 13 +++++++++++++
 include/uapi/drm/i915_drm.h             |  5 +++--
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index b16b8e226e40..1724fa9c481e 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -808,6 +808,7 @@ i915_gem_userptr_ioctl(struct drm_device *dev, void *data, struct drm_file *file
 	}
 
 	if (args->flags & ~(I915_USERPTR_READ_ONLY |
+			    I915_USERPTR_PROBE |
 			    I915_USERPTR_UNSYNCHRONIZED))
 		return -EINVAL;
 
@@ -825,6 +826,18 @@ i915_gem_userptr_ioctl(struct drm_device *dev, void *data, struct drm_file *file
 		return -ENODEV;
 	}
 
+	if (args->flags & I915_USERPTR_PROBE) {
+		/*
+		 * Check that the range pointed to represents real struct
+		 * pages and not iomappings (at *this* moment in time!)
+		 */
+		down_read(&current->mm->mmap_sem);
+		ret = probe_range(current->mm, args->user_ptr, args->user_size);
+		up_read(&current->mm->mmap_sem);
+		if (ret)
+			return ret;
+	}
+
 	obj = i915_gem_object_alloc(dev_priv);
 	if (obj == NULL)
 		return -ENOMEM;
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 866ef066c40d..6487aac3f2f5 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -1438,8 +1438,9 @@ struct drm_i915_gem_userptr {
 	__u64 user_ptr;
 	__u64 user_size;
 	__u32 flags;
-#define I915_USERPTR_READ_ONLY 0x1
-#define I915_USERPTR_UNSYNCHRONIZED 0x80000000
+#define I915_USERPTR_READ_ONLY		0x1
+#define I915_USERPTR_PROBE		0x2
+#define I915_USERPTR_UNSYNCHRONIZED	0x80000000
 	/**
 	 * Returned handle for the object.
 	 *
-- 
2.15.1