Op 23-07-2021 om 13:34 schreef Matthew Auld:
> From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
>
> 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: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Matthew Auld <matthew.auld@xxxxxxxxx>
> Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
> Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
> Cc: Jordan Justen <jordan.l.justen@xxxxxxxxx>
> Cc: Kenneth Graunke <kenneth@xxxxxxxxxxxxx>
> Cc: Jason Ekstrand <jason@xxxxxxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: Ramalingam C <ramalingam.c@xxxxxxxxx>
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> Acked-by: Kenneth Graunke <kenneth@xxxxxxxxxxxxx>
> Reviewed-by: Jason Ekstrand <jason@xxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 41 ++++++++++++++++++++-
> drivers/gpu/drm/i915/i915_getparam.c | 1 +
> include/uapi/drm/i915_drm.h | 20 ++++++++++
> 3 files changed, 61 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..468a7a617fbf 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> @@ -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)
> diff --git a/drivers/gpu/drm/i915/i915_getparam.c b/drivers/gpu/drm/i915/i915_getparam.c
> index 24e18219eb50..bbb7cac43eb4 100644
> --- a/drivers/gpu/drm/i915/i915_getparam.c
> +++ b/drivers/gpu/drm/i915/i915_getparam.c
> @@ -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
> diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
> index 975087553ea0..0d290535a6e5 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 {
> @@ -2222,12 +2225,29 @@ 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.
Could we use _VALIDATE instead of probe? Or at least pin the pages as well, so we don't have to do it later?
We already have i915_gem_object_userptr_validate, no need to dupe it.
