[PATCH 3/4] drm/i915/userptr: Probe existence of backing struct pages upon creation
Jason Ekstrand
jason at jlekstrand.net
Wed Jul 21 20:27:48 UTC 2021
On Thu, Jul 15, 2021 at 5:16 AM Matthew Auld <matthew.auld at intel.com> wrote:
>
> 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)
Why isn't this > end? Are we somehow guaranteed that one vma covers
the entire range?
> + 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
>
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