Commit b65a9489 authored by Chris Wilson's avatar Chris Wilson Committed by Maarten Lankhorst
Browse files

drm/i915/userptr: Probe existence of backing struct pages upon creation 



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 we 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 PROBE flag, so userspace can easily
  check if the kernel supports it(Jason).
- use mmap_read_{lock, unlock}.
- add some kernel-doc.
v3:
- In the docs also mention that PROBE doesn't guarantee that the pages
  will remain valid by the time they are actually used(Tvrtko).
- Add a small comment for the hole finding logic(Jason).
- Move the param next to all the other params which just return true.

Testcase: igt/gem_userptr_blits/probe
Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: default avatarMatthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Kenneth Graunke <kenneth@whitecape.org>
Cc: Jason Ekstrand <jason@jlekstrand.net>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ramalingam C <ramalingam.c@intel.com>
Reviewed-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
Acked-by: default avatarKenneth Graunke <kenneth@whitecape.org>
Reviewed-by: default avatarJason Ekstrand <jason@jlekstrand.net>
Acked-by: default avatarMaarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: default avatarMaarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210723113405.427004-1-matthew.auld@intel.com
parent 8e02cceb

drivers/gpu/drm/i915/gem/i915_gem_userptr.c

+40 −1
Original line number Diff line number Diff line
@@ -422,6 +422,34 @@ 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) {

		/* Check for holes, note that we also update the addr below */

		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 +505,8 @@ 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 +533,16 @@ 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)

drivers/gpu/drm/i915/i915_getparam.c

+1 −0
Original line number Diff line number Diff line
@@ -134,6 +134,7 @@ int i915_getparam_ioctl(struct drm_device *dev, void *data, 
	case I915_PARAM_HAS_EXEC_FENCE_ARRAY:

	case I915_PARAM_HAS_EXEC_SUBMIT_FENCE:

	case I915_PARAM_HAS_EXEC_TIMELINE_FENCES:

	case I915_PARAM_HAS_USERPTR_PROBE:

		/* For the time being all of these are always true;

		 * if some supported hardware does not have one of these

		 * features this value needs to be provided from

include/uapi/drm/i915_drm.h

+20 −0
Original line number Diff line number Diff line
@@ -683,6 +683,9 @@ 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 {
@@ -2231,12 +2234,29 @@ 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, and also doesn't

	 * guarantee that the object will remain valid when the object is

	 * eventually used.

	 *

	 * 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.