[PATCH] drm/i915: Allow userptr backchannel for passing aroung GTT mappings

[PATCH] drm/i915: Allow userptr backchannel for passing aroung GTT mappings

[Chris Wilson]

Once userptr becomes part of client API, it is almost a certainly that
eventually someone will try to create a new object from a mapping of
another client object, e.g.

new = vaImport(vaMap(old, &size), size);

(using a hypothethical API, not meaning to pick on anyone!)

Since this is actually fairly safe to implement and to allow (since it
is within a single process space and the memory access passes the
standard permissions test) let us not limit the Client possibilities.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Gwenole Beauchesne <gwenole.beauchesne@intel.com>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
---
 drivers/gpu/drm/i915/i915_gem_userptr.c | 46 ++++++++++++++++++++++++++++++---
 1 file changed, 43 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index d96276caab49..8031ebe424fd 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -750,6 +750,35 @@ static const struct drm_i915_gem_object_ops i915_gem_userptr_ops = {
 	.release = i915_gem_userptr_release,
 };
 
+static struct drm_i915_gem_object *
+find_object_from_vma(struct drm_device *dev,
+		     struct drm_i915_gem_userptr *args)
+{
+	struct drm_i915_gem_object *obj = NULL;
+	struct vm_area_struct *vma;
+
+	down_read(&current->mm->mmap_sem);
+	vma = find_vma(current->mm, args->user_ptr);
+	if (vma == NULL)
+		goto out;
+
+	if (vma->vm_ops != dev->driver->gem_vm_ops)
+		goto out;
+
+	if (vma->vm_start != args->user_ptr ||
+	    vma->vm_end != args->user_ptr + args->user_size) {
+		obj = ERR_PTR(-EINVAL);
+		goto out;
+	}
+
+	obj = to_intel_bo(vma->vm_private_data);
+	drm_gem_object_reference(obj);
+
+out:
+	up_read(&current->mm->mmap_sem);
+	return obj;
+}
+
 /**
  * Creates a new mm object that wraps some normal memory from the process
  * context - user memory.
@@ -757,8 +786,11 @@ static const struct drm_i915_gem_object_ops i915_gem_userptr_ops = {
  * We impose several restrictions upon the memory being mapped
  * into the GPU.
  * 1. It must be page aligned (both start/end addresses, i.e ptr and size).
- * 2. It must be normal system memory, not a pointer into another map of IO
- *    space (e.g. it must not be a GTT mmapping of another object).
+ * 2. It must either be:
+ *    a) normal system memory, not a pointer into another map of IO
+ *       space (e.g. it must not be part of a GTT mmapping of another object).
+ *    b) a pointer to the complete GTT mmap of another object in your
+ *       address space.
  * 3. We only allow a bo as large as we could in theory map into the GTT,
  *    that is we limit the size to the total size of the GTT.
  * 4. The bo is marked as being snoopable. The backing pages are left
@@ -812,6 +844,14 @@ i915_gem_userptr_ioctl(struct drm_device *dev, void *data, struct drm_file *file
 		return -ENODEV;
 	}
 
+	obj = find_object_from_vma(dev, args);
+	if (obj) {
+		if (IS_ERR(obj))
+			return PTR_ERR(obj);
+		else
+			goto out;
+	}
+
 	obj = i915_gem_object_alloc(dev);
 	if (obj == NULL)
 		return -ENOMEM;
@@ -833,7 +873,7 @@ i915_gem_userptr_ioctl(struct drm_device *dev, void *data, struct drm_file *file
 	if (ret == 0)
 		ret = i915_gem_userptr_init__mmu_notifier(obj, args->flags);
 	if (ret == 0)
-		ret = drm_gem_handle_create(file, &obj->base, &handle);
+out:		 ret = drm_gem_handle_create(file, &obj->base, &handle);
 
 	/* drop reference from allocate - handle holds it now */
 	drm_gem_object_unreference_unlocked(&obj->base);
-- 
2.1.4

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Re: [PATCH] drm/i915: Allow userptr backchannel for passing aroung GTT mappings

[Tvrtko Ursulin]

Hi,

Typo in subject, then below.

On 04/02/2015 04:04 PM, Chris Wilson wrote:
> Once userptr becomes part of client API, it is almost a certainly that
> eventually someone will try to create a new object from a mapping of
> another client object, e.g.
>
> new = vaImport(vaMap(old, &size), size);
>
> (using a hypothethical API, not meaning to pick on anyone!)
>
> Since this is actually fairly safe to implement and to allow (since it
> is within a single process space and the memory access passes the
> standard permissions test) let us not limit the Client possibilities.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Gwenole Beauchesne <gwenole.beauchesne@intel.com>
> Cc: Michał Winiarski <michal.winiarski@intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>   drivers/gpu/drm/i915/i915_gem_userptr.c | 46 ++++++++++++++++++++++++++++++---
>   1 file changed, 43 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
> index d96276caab49..8031ebe424fd 100644
> --- a/drivers/gpu/drm/i915/i915_gem_userptr.c
> +++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
> @@ -750,6 +750,35 @@ static const struct drm_i915_gem_object_ops i915_gem_userptr_ops = {
>   	.release = i915_gem_userptr_release,
>   };
>
> +static struct drm_i915_gem_object *
> +find_object_from_vma(struct drm_device *dev,
> +		     struct drm_i915_gem_userptr *args)
> +{
> +	struct drm_i915_gem_object *obj = NULL;
> +	struct vm_area_struct *vma;
> +
> +	down_read(&current->mm->mmap_sem);
> +	vma = find_vma(current->mm, args->user_ptr);
> +	if (vma == NULL)
> +		goto out;
> +
> +	if (vma->vm_ops != dev->driver->gem_vm_ops)
> +		goto out;
> +
> +	if (vma->vm_start != args->user_ptr ||
> +	    vma->vm_end != args->user_ptr + args->user_size) {
> +		obj = ERR_PTR(-EINVAL);
> +		goto out;
> +	}
> +
> +	obj = to_intel_bo(vma->vm_private_data);
> +	drm_gem_object_reference(obj);

Hm, can't this race with last unreference in general, and with cleanup 
worker with userptr objects?

> +
> +out:
> +	up_read(&current->mm->mmap_sem);
> +	return obj;
> +}
> +
>   /**
>    * Creates a new mm object that wraps some normal memory from the process
>    * context - user memory.
> @@ -757,8 +786,11 @@ static const struct drm_i915_gem_object_ops i915_gem_userptr_ops = {
>    * We impose several restrictions upon the memory being mapped
>    * into the GPU.
>    * 1. It must be page aligned (both start/end addresses, i.e ptr and size).
> - * 2. It must be normal system memory, not a pointer into another map of IO
> - *    space (e.g. it must not be a GTT mmapping of another object).
> + * 2. It must either be:
> + *    a) normal system memory, not a pointer into another map of IO
> + *       space (e.g. it must not be part of a GTT mmapping of another object).
> + *    b) a pointer to the complete GTT mmap of another object in your
> + *       address space.
>    * 3. We only allow a bo as large as we could in theory map into the GTT,
>    *    that is we limit the size to the total size of the GTT.
>    * 4. The bo is marked as being snoopable. The backing pages are left
> @@ -812,6 +844,14 @@ i915_gem_userptr_ioctl(struct drm_device *dev, void *data, struct drm_file *file
>   		return -ENODEV;
>   	}
>
> +	obj = find_object_from_vma(dev, args);
> +	if (obj) {
> +		if (IS_ERR(obj))
> +			return PTR_ERR(obj);
> +		else
> +			goto out;
> +	}
> +
>   	obj = i915_gem_object_alloc(dev);
>   	if (obj == NULL)
>   		return -ENOMEM;
> @@ -833,7 +873,7 @@ i915_gem_userptr_ioctl(struct drm_device *dev, void *data, struct drm_file *file
>   	if (ret == 0)
>   		ret = i915_gem_userptr_init__mmu_notifier(obj, args->flags);
>   	if (ret == 0)
> -		ret = drm_gem_handle_create(file, &obj->base, &handle);
> +out:		 ret = drm_gem_handle_create(file, &obj->base, &handle);
>
>   	/* drop reference from allocate - handle holds it now */
>   	drm_gem_object_unreference_unlocked(&obj->base);

Thing I don't like is how the user of this has no idea what kind of 
object it "imported". Maybe it doesn't matter, hm. Need to think about 
it more.

Regards,

Tvrtko
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Re: [PATCH] drm/i915: Allow userptr backchannel for passing aroung GTT mappings

[Chris Wilson]

On Thu, Apr 02, 2015 at 05:11:58PM +0100, Tvrtko Ursulin wrote:
> >+static struct drm_i915_gem_object *
> >+find_object_from_vma(struct drm_device *dev,
> >+		     struct drm_i915_gem_userptr *args)
> >+{
> >+	struct drm_i915_gem_object *obj = NULL;
> >+	struct vm_area_struct *vma;
> >+
> >+	down_read(&current->mm->mmap_sem);
> >+	vma = find_vma(current->mm, args->user_ptr);
> >+	if (vma == NULL)
> >+		goto out;
> >+
> >+	if (vma->vm_ops != dev->driver->gem_vm_ops)
> >+		goto out;
> >+
> >+	if (vma->vm_start != args->user_ptr ||
> >+	    vma->vm_end != args->user_ptr + args->user_size) {
> >+		obj = ERR_PTR(-EINVAL);
> >+		goto out;
> >+	}
> >+
> >+	obj = to_intel_bo(vma->vm_private_data);
> >+	drm_gem_object_reference(obj);
> 
> Hm, can't this race with last unreference in general, and with
> cleanup worker with userptr objects?

The vma holds a reference to the object and that reference is dropped
whilst holding down_write(current->mm->mmap_sem), hence I think the
down_read(current->mm->mmap_sem) is sufficient locking to acquire a
reference for ourselves.

> >+out:		 ret = drm_gem_handle_create(file, &obj->base, &handle);
> >
> >  	/* drop reference from allocate - handle holds it now */
> >  	drm_gem_object_unreference_unlocked(&obj->base);
> 
> Thing I don't like is how the user of this has no idea what kind of
> object it "imported". Maybe it doesn't matter, hm. Need to think
> about it more.

Indeed. But since the userptr is a strict subset of the general bo, if
they follow the rules for userptr bo then they won't notice a
difference. read/writes into the memory block are coherent (since the
pointer is wc) so as far the caller is concerned I think it just ends up
being slower cpu side, faster gpu side than a system memory snooped
userptr bo.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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Re: [PATCH] drm/i915: Allow userptr backchannel for passing aroung GTT mappings

[Tvrtko Ursulin]

On 04/02/2015 05:27 PM, Chris Wilson wrote:
> On Thu, Apr 02, 2015 at 05:11:58PM +0100, Tvrtko Ursulin wrote:
>>> +static struct drm_i915_gem_object *
>>> +find_object_from_vma(struct drm_device *dev,
>>> +		     struct drm_i915_gem_userptr *args)
>>> +{
>>> +	struct drm_i915_gem_object *obj = NULL;
>>> +	struct vm_area_struct *vma;
>>> +
>>> +	down_read(&current->mm->mmap_sem);
>>> +	vma = find_vma(current->mm, args->user_ptr);
>>> +	if (vma == NULL)
>>> +		goto out;
>>> +
>>> +	if (vma->vm_ops != dev->driver->gem_vm_ops)
>>> +		goto out;
>>> +
>>> +	if (vma->vm_start != args->user_ptr ||
>>> +	    vma->vm_end != args->user_ptr + args->user_size) {
>>> +		obj = ERR_PTR(-EINVAL);
>>> +		goto out;
>>> +	}
>>> +
>>> +	obj = to_intel_bo(vma->vm_private_data);
>>> +	drm_gem_object_reference(obj);
>>
>> Hm, can't this race with last unreference in general, and with
>> cleanup worker with userptr objects?
>
> The vma holds a reference to the object and that reference is dropped
> whilst holding down_write(current->mm->mmap_sem), hence I think the
> down_read(current->mm->mmap_sem) is sufficient locking to acquire a
> reference for ourselves.

Yes, I completely forgot about this little detail. :)

>>> +out:		 ret = drm_gem_handle_create(file, &obj->base, &handle);
>>>
>>>   	/* drop reference from allocate - handle holds it now */
>>>   	drm_gem_object_unreference_unlocked(&obj->base);
>>
>> Thing I don't like is how the user of this has no idea what kind of
>> object it "imported". Maybe it doesn't matter, hm. Need to think
>> about it more.
>
> Indeed. But since the userptr is a strict subset of the general bo, if
> they follow the rules for userptr bo then they won't notice a
> difference. read/writes into the memory block are coherent (since the
> pointer is wc) so as far the caller is concerned I think it just ends up
> being slower cpu side, faster gpu side than a system memory snooped
> userptr bo.

Is access to non-userptr bo's interesting to users of this - could we 
reject that and not lose out?

Regards,

Tvrtko
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Re: [PATCH] drm/i915: Allow userptr backchannel for passing aroung GTT mappings

[shuang.he]

Tested-By: PRC QA PRTS (Patch Regression Test System Contact: shuang.he@intel.com)
Task id: 6123
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
PNV                 -1              272/272              271/272
ILK                 -1              302/302              301/302
SNB                 -1              303/303              302/303
IVB                 -1              338/338              337/338
BYT                 -2              287/287              285/287
HSW                 -1              361/361              360/361
BDW                 -1              308/308              307/308
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
*PNV  igt@gem_userptr_blits@invalid-gtt-mapping      PASS(2)      FAIL(2)
*ILK  igt@gem_userptr_blits@invalid-gtt-mapping      PASS(2)      FAIL(2)
*SNB  igt@gem_userptr_blits@invalid-gtt-mapping      PASS(2)      FAIL(2)
*IVB  igt@gem_userptr_blits@invalid-gtt-mapping      PASS(2)      FAIL(2)
*BYT  igt@gem_exec_bad_domains@conflicting-write-domain      PASS(15)      FAIL(1)PASS(1)
*BYT  igt@gem_userptr_blits@invalid-gtt-mapping      PASS(2)      FAIL(2)
*HSW  igt@gem_userptr_blits@invalid-gtt-mapping      PASS(2)      FAIL(2)
*BDW  igt@gem_userptr_blits@invalid-gtt-mapping      PASS(2)      FAIL(2)
Note: You need to pay more attention to line start with '*'
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Re: [PATCH] drm/i915: Allow userptr backchannel for passing aroung GTT mappings

[Daniel Vetter]

On Thu, Apr 02, 2015 at 04:04:14PM +0100, Chris Wilson wrote:
> Once userptr becomes part of client API, it is almost a certainly that
> eventually someone will try to create a new object from a mapping of
> another client object, e.g.
> 
> new = vaImport(vaMap(old, &size), size);
> 
> (using a hypothethical API, not meaning to pick on anyone!)
> 
> Since this is actually fairly safe to implement and to allow (since it
> is within a single process space and the memory access passes the
> standard permissions test) let us not limit the Client possibilities.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Gwenole Beauchesne <gwenole.beauchesne@intel.com>
> Cc: Michał Winiarski <michal.winiarski@intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Thus far all the apis are very explicit in stating that you can only slurp
in anything that's allocated with malloc and friends. Also usually this
means we're dealing with tiled memory which looks linear, so I'm not sure
how this will work.
-Daniel

> ---
>  drivers/gpu/drm/i915/i915_gem_userptr.c | 46 ++++++++++++++++++++++++++++++---
>  1 file changed, 43 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
> index d96276caab49..8031ebe424fd 100644
> --- a/drivers/gpu/drm/i915/i915_gem_userptr.c
> +++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
> @@ -750,6 +750,35 @@ static const struct drm_i915_gem_object_ops i915_gem_userptr_ops = {
>  	.release = i915_gem_userptr_release,
>  };
>  
> +static struct drm_i915_gem_object *
> +find_object_from_vma(struct drm_device *dev,
> +		     struct drm_i915_gem_userptr *args)
> +{
> +	struct drm_i915_gem_object *obj = NULL;
> +	struct vm_area_struct *vma;
> +
> +	down_read(&current->mm->mmap_sem);
> +	vma = find_vma(current->mm, args->user_ptr);
> +	if (vma == NULL)
> +		goto out;
> +
> +	if (vma->vm_ops != dev->driver->gem_vm_ops)
> +		goto out;
> +
> +	if (vma->vm_start != args->user_ptr ||
> +	    vma->vm_end != args->user_ptr + args->user_size) {
> +		obj = ERR_PTR(-EINVAL);
> +		goto out;
> +	}
> +
> +	obj = to_intel_bo(vma->vm_private_data);
> +	drm_gem_object_reference(obj);
> +
> +out:
> +	up_read(&current->mm->mmap_sem);
> +	return obj;
> +}
> +
>  /**
>   * Creates a new mm object that wraps some normal memory from the process
>   * context - user memory.
> @@ -757,8 +786,11 @@ static const struct drm_i915_gem_object_ops i915_gem_userptr_ops = {
>   * We impose several restrictions upon the memory being mapped
>   * into the GPU.
>   * 1. It must be page aligned (both start/end addresses, i.e ptr and size).
> - * 2. It must be normal system memory, not a pointer into another map of IO
> - *    space (e.g. it must not be a GTT mmapping of another object).
> + * 2. It must either be:
> + *    a) normal system memory, not a pointer into another map of IO
> + *       space (e.g. it must not be part of a GTT mmapping of another object).
> + *    b) a pointer to the complete GTT mmap of another object in your
> + *       address space.
>   * 3. We only allow a bo as large as we could in theory map into the GTT,
>   *    that is we limit the size to the total size of the GTT.
>   * 4. The bo is marked as being snoopable. The backing pages are left
> @@ -812,6 +844,14 @@ i915_gem_userptr_ioctl(struct drm_device *dev, void *data, struct drm_file *file
>  		return -ENODEV;
>  	}
>  
> +	obj = find_object_from_vma(dev, args);
> +	if (obj) {
> +		if (IS_ERR(obj))
> +			return PTR_ERR(obj);
> +		else
> +			goto out;
> +	}
> +
>  	obj = i915_gem_object_alloc(dev);
>  	if (obj == NULL)
>  		return -ENOMEM;
> @@ -833,7 +873,7 @@ i915_gem_userptr_ioctl(struct drm_device *dev, void *data, struct drm_file *file
>  	if (ret == 0)
>  		ret = i915_gem_userptr_init__mmu_notifier(obj, args->flags);
>  	if (ret == 0)
> -		ret = drm_gem_handle_create(file, &obj->base, &handle);
> +out:		 ret = drm_gem_handle_create(file, &obj->base, &handle);
>  
>  	/* drop reference from allocate - handle holds it now */
>  	drm_gem_object_unreference_unlocked(&obj->base);
> -- 
> 2.1.4
> 
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH] drm/i915: Allow userptr backchannel for passing aroung GTT mappings

[Chris Wilson]

On Tue, Apr 07, 2015 at 10:53:20AM +0200, Daniel Vetter wrote:
> On Thu, Apr 02, 2015 at 04:04:14PM +0100, Chris Wilson wrote:
> > Once userptr becomes part of client API, it is almost a certainly that
> > eventually someone will try to create a new object from a mapping of
> > another client object, e.g.
> > 
> > new = vaImport(vaMap(old, &size), size);
> > 
> > (using a hypothethical API, not meaning to pick on anyone!)
> > 
> > Since this is actually fairly safe to implement and to allow (since it
> > is within a single process space and the memory access passes the
> > standard permissions test) let us not limit the Client possibilities.
> > 
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > Cc: Gwenole Beauchesne <gwenole.beauchesne@intel.com>
> > Cc: Michał Winiarski <michal.winiarski@intel.com>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> 
> Thus far all the apis are very explicit in stating that you can only slurp
> in anything that's allocated with malloc and friends. Also usually this
> means we're dealing with tiled memory which looks linear, so I'm not sure
> how this will work.

The user doesn't know the object it tiled, all they have is a linear
mapping. The kernel doesn't care either, all it sees is a bo. The idea
is to simply enable a likely usecase that just works.
-Chris

-- 
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