Re: [Intel-gfx] [PATCH] drm/i915/userptr: Probe existence of backing struct pages upon creation

[Jason Ekstrand <jason@jlekstrand.net>]

On Mon, Jul 26, 2021 at 3:06 AM Matthew Auld
<matthew.william.auld@gmail.com> wrote:
>
> On Fri, 23 Jul 2021 at 18:48, Jason Ekstrand <jason@jlekstrand.net> wrote:
> >
> > https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12044
>
> Cool, is that ready to go? i.e can we start merging the kernel + IGT side.

Yes, it's all reviewed.  Though, it sounds like Maarten had a comment
so we should settle on that before landing.

> >
> > On Fri, Jul 23, 2021 at 6:35 AM Matthew Auld <matthew.auld@intel.com> wrote:
> > >
> > > From: Chris Wilson <chris@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 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@chris-wilson.co.uk>
> > > Signed-off-by: Matthew 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: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> > > Acked-by: Kenneth Graunke <kenneth@whitecape.org>
> > > Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
> > > ---
> > >  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.
> > > --
> > > 2.26.3
> > >
> > _______________________________________________
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> > Intel-gfx@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
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