[PATCH] drm/i915/userptr: Probe existence of backing struct pages upon creation
Jason Ekstrand
jason at jlekstrand.net
Mon Jul 26 15:14:32 UTC 2021
On Mon, Jul 26, 2021 at 3:31 AM Maarten Lankhorst
<maarten.lankhorst at linux.intel.com> wrote:
>
> Op 23-07-2021 om 13:34 schreef 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 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 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>
> > Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > Acked-by: Kenneth Graunke <kenneth at whitecape.org>
> > Reviewed-by: Jason Ekstrand <jason at 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.
>
> Could we use _VALIDATE instead of probe? Or at least pin the pages as well, so we don't have to do it later?
I only care that the name matches what it does. _VALIDATE sounds like
it does a full validation of everything such that, if the import
succeeds, execbuf will as well. If we pin the pages at the same time,
maybe that's true? _PROBE, on the other hand, sounds a lot more like
a one-time best-effort check which may race with other stuff and
doesn't guarantee future success. That's in line with what the
current patch does.
> We already have i915_gem_object_userptr_validate, no need to dupe it.
I have no opinion on this.
--Jason
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