[Intel-gfx] [PATCH] drm/i915/userptr: Probe existence of backing struct pages upon creation
Jason Ekstrand
jason at jlekstrand.net
Tue Aug 3 15:45:44 UTC 2021
On Tue, Aug 3, 2021 at 10:09 AM Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> On Wed, Jul 28, 2021 at 4:22 PM Matthew Auld
> <matthew.william.auld at gmail.com> wrote:
> >
> > On Mon, 26 Jul 2021 at 17:10, Tvrtko Ursulin
> > <tvrtko.ursulin at linux.intel.com> wrote:
> > >
> > >
> > > On 26/07/2021 16:14, Jason Ekstrand wrote:
> > > > 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
> > >
> > > No it is not possible to guarantee backing store remains valid until
> > > execbuf.
> > >
> > > > 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.
> > >
> > > I was actually suggesting the same as Maarten here - that we should add
> > > a "populate" flag. But opinion was that was not desired - please look
> > > for the older threads to see the reasoning there.
> >
> > So how should we proceed here? Maarten?
>
> I honestly don't care, and I think the probe flag here is perfectly
> fine. Reasons for that:
> - we don't have an immediate allocation flag for buffer creation
> either. So if there's a need we need a flag for this across the board,
> not just userptr, and a clear userspace ask
Both Mesa drivers would probably set that flag if we had it and it
demonstrated any perf benefits, FWIW. However, I think it's fine if
that's a separate flag. Also, I don't know that the perf benefits are
all that great. We should get most of those benefits from VM_BIND
anyway.
> - it's a fundamentally racy test anyway, userspace can munmap or map
> something else and then it will fail. So we really don't gain anything
> by pinning pages because by the time we go into execbuf they might be
> invalidated already - checking the vmas for VM_SPECIAL is perfectly
> good enough.
> - we can always change the implementation later on too.
>
> Hence why I think PROBE is the semantics we want/need here. Can we get
> some acks/reviews here or is this really a significant enough bikeshed
> that we need to hold up dg1 pciids for them?
I don't care. I've already reviewed the patch.
--Jason
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