[PATCH 25/31] 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 | 38 +++++++++++++++++++++++++++++++++
 include/uapi/drm/i915_drm.h             |  5 +++--
 2 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index 382a77a1097e..841ae4caf768 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -721,6 +721,33 @@ static const struct drm_i915_gem_object_ops i915_gem_userptr_ops = {
 	.release = i915_gem_userptr_release,
 };
 
+static int
+probe_range(struct mm_struct *mm, unsigned long addr, unsigned long len)
+{
+	const unsigned long end = addr + len;
+	struct vm_area_struct *vma;
+	int ret = -EFAULT;
+
+	down_read(&mm->mmap_sem);
+	for (vma = find_vma(mm, addr); vma; vma = vma->vm_next) {
+		if (vma->vm_start > addr)
+			break;
+
+		if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
+			break;
+
+		if (vma->vm_end >= end) {
+			ret = 0;
+			break;
+		}
+
+		addr = vma->vm_end;
+	}
+	up_read(&mm->mmap_sem);
+
+	return ret;
+}
+
 /**
  * Creates a new mm object that wraps some normal memory from the process
  * context - user memory.
@@ -773,6 +800,7 @@ 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;
 
@@ -790,6 +818,16 @@ 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!)
+		 */
+		ret = probe_range(current->mm, args->user_ptr, args->user_size);
+		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 536ee4febd74..7381342602ab 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -1429,8 +1429,9 @@ 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.
 	 *
-- 
2.15.0