[PATCH] drm/i915/userptr: Probe existence of backing struct pages upon creation
Tvrtko Ursulin
tvrtko.ursulin at linux.intel.com
Mon Jul 26 16:10:43 UTC 2021
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.
Regards,
Tvrtko
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