[PATCH 3/4] drm/i915/userptr: Probe existence of backing struct pages upon creation

[Matthew Auld]

From: Chris Wilson <chris at chris-wilson.co.uk>

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...

With discrete are going to drop support for set_domain(), so offering a
way to probe the pages, without having to resort to dummy batches has
been requested.

v2:
- add new query param for the PROPBE flag, so userspace can easily
  check if the kernel supports it(Jason).
- use mmap_read_{lock, unlock}.
- add some kernel-doc.

Testcase: igt/gem_userptr_blits/probe
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Matthew Auld <matthew.auld at intel.com>
Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
Cc: Jordan Justen <jordan.l.justen at intel.com>
Cc: Kenneth Graunke <kenneth at whitecape.org>
Cc: Jason Ekstrand <jason at jlekstrand.net>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Ramalingam C <ramalingam.c at intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 40 ++++++++++++++++++++-
 drivers/gpu/drm/i915/i915_getparam.c        |  3 ++
 include/uapi/drm/i915_drm.h                 | 18 ++++++++++
 3 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
index 56edfeff8c02..fd6880328596 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
@@ -422,6 +422,33 @@ static const struct drm_i915_gem_object_ops i915_gem_userptr_ops = {
 
 #endif
 
+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;
+
+	mmap_read_lock(mm);
+	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;
+	}
+	mmap_read_unlock(mm);
+
+	return ret;
+}
+
 /*
  * Creates a new mm object that wraps some normal memory from the process
  * context - user memory.
@@ -477,7 +504,8 @@ i915_gem_userptr_ioctl(struct drm_device *dev,
 	}
 
 	if (args->flags & ~(I915_USERPTR_READ_ONLY |
-			    I915_USERPTR_UNSYNCHRONIZED))
+			    I915_USERPTR_UNSYNCHRONIZED |
+			    I915_USERPTR_PROBE))
 		return -EINVAL;
 
 	if (i915_gem_object_size_2big(args->user_size))
@@ -504,6 +532,16 @@ i915_gem_userptr_ioctl(struct drm_device *dev,
 			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;
+	}
+
 #ifdef CONFIG_MMU_NOTIFIER
 	obj = i915_gem_object_alloc();
 	if (obj == NULL)
diff --git a/drivers/gpu/drm/i915/i915_getparam.c b/drivers/gpu/drm/i915/i915_getparam.c
index 24e18219eb50..d6d2e1a10d14 100644
--- a/drivers/gpu/drm/i915/i915_getparam.c
+++ b/drivers/gpu/drm/i915/i915_getparam.c
@@ -163,6 +163,9 @@ int i915_getparam_ioctl(struct drm_device *dev, void *data,
 	case I915_PARAM_PERF_REVISION:
 		value = i915_perf_ioctl_version();
 		break;
+	case I915_PARAM_HAS_USERPTR_PROBE:
+		value = true;
+		break;
 	default:
 		DRM_DEBUG("Unknown parameter %d\n", param->param);
 		return -EINVAL;
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index e20eeeca7a1c..2e4112bf4d38 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -674,6 +674,9 @@ typedef struct drm_i915_irq_wait {
  */
 #define I915_PARAM_HAS_EXEC_TIMELINE_FENCES 55
 
+/* Query if the kernel supports the I915_USERPTR_PROBE flag. */
+#define I915_PARAM_HAS_USERPTR_PROBE 56
+
 /* Must be kept compact -- no holes and well documented */
 
 typedef struct drm_i915_getparam {
@@ -2178,12 +2181,27 @@ struct drm_i915_gem_userptr {
 	 * through the GTT. If the HW can't support readonly access, an error is
 	 * returned.
 	 *
+	 * I915_USERPTR_PROBE:
+	 *
+	 * Probe the provided @user_ptr range and validate that the @user_ptr is
+	 * indeed pointing to normal memory and that the range is also valid.
+	 * For example if some garbage address is given to the kernel, then this
+	 * should complain.
+	 *
+	 * Returns -EFAULT if the probe failed.
+	 *
+	 * Note that this doesn't populate the backing pages.
+	 *
+	 * The kernel supports this feature if I915_PARAM_HAS_USERPTR_PROBE
+	 * returns a non-zero value.
+	 *
 	 * I915_USERPTR_UNSYNCHRONIZED:
 	 *
 	 * NOT USED. Setting this flag will result in an error.
 	 */
 	__u32 flags;
 #define I915_USERPTR_READ_ONLY 0x1
+#define I915_USERPTR_PROBE 0x2
 #define I915_USERPTR_UNSYNCHRONIZED 0x80000000
 	/**
 	 * @handle: Returned handle for the object.
-- 
2.26.3