Re: [Freedreno] [PATCH 2/2] drm/msm: Add MSM_WAIT_IOVA ioctl

[Jordan Crouse <jcrouse@codeaurora.org>]

On Mon, Jan 13, 2020 at 10:36:05AM -0500, Brian Ho wrote:
> Implements an ioctl to wait until a value at a given iova is greater
> than or equal to a supplied value.
> 
> This will initially be used by turnip (open-source Vulkan driver for
> QC in mesa) for occlusion queries where the userspace driver can
> block on a query becoming available before continuing via
> vkGetQueryPoolResults.
> 
> Signed-off-by: Brian Ho <brian@brkho.com>
> ---
>  drivers/gpu/drm/msm/msm_drv.c | 63 +++++++++++++++++++++++++++++++++--
>  include/uapi/drm/msm_drm.h    | 13 ++++++++
>  2 files changed, 74 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
> index c84f0a8b3f2c..dcc46874a5a2 100644
> --- a/drivers/gpu/drm/msm/msm_drv.c
> +++ b/drivers/gpu/drm/msm/msm_drv.c
> @@ -36,10 +36,11 @@
>   *           MSM_GEM_INFO ioctl.
>   * - 1.4.0 - softpin, MSM_RELOC_BO_DUMP, and GEM_INFO support to set/get
>   *           GEM object's debug name
> - * - 1.5.0 - Add SUBMITQUERY_QUERY ioctl
> + * - 1.5.0 - Add SUBMITQUEUE_QUERY ioctl
> + * - 1.6.0 - Add WAIT_IOVA ioctl
>   */
>  #define MSM_VERSION_MAJOR	1
> -#define MSM_VERSION_MINOR	5
> +#define MSM_VERSION_MINOR	6
>  #define MSM_VERSION_PATCHLEVEL	0
>  
>  static const struct drm_mode_config_funcs mode_config_funcs = {
> @@ -952,6 +953,63 @@ static int msm_ioctl_submitqueue_close(struct drm_device *dev, void *data,
>  	return msm_submitqueue_remove(file->driver_priv, id);
>  }
>  
> +static int msm_ioctl_wait_iova(struct drm_device *dev, void *data,
> +		struct drm_file *file)
> +{
> +	struct msm_drm_private *priv = dev->dev_private;
> +	struct drm_gem_object *obj;
> +	struct drm_msm_wait_iova *args = data;
> +	ktime_t timeout = to_ktime(args->timeout);
> +	unsigned long remaining_jiffies = timeout_to_jiffies(&timeout);
> +	struct msm_gpu *gpu = priv->gpu;
> +	void *base_vaddr;
> +	uint64_t *vaddr;
> +	int ret;
> +
> +	if (args->pad)
> +		return -EINVAL;
> +
> +	if (!gpu)
> +		return 0;

If the GPU isn't up, it should be an error since this macro is specifically
designed for just the GPU (though, I suppose the display *COULD* use it to watch
a memory mapped register or something).

> +
> +	obj = drm_gem_object_lookup(file, args->handle);
> +	if (!obj)
> +		return -ENOENT;
> +
> +	base_vaddr = msm_gem_get_vaddr(obj);
> +	if (IS_ERR(base_vaddr)) {
> +		ret = PTR_ERR(base_vaddr);
> +		goto err_put_gem_object;
> +	}
> +	if (args->offset + sizeof(*vaddr) > obj->size) {

There is a chance to trigger a u64 overflow here resulting in an arbitrary (ish)
vaddr two lines below.


> +		ret = -EINVAL;
> +		goto err_put_vaddr;
> +	}

You can check this before getting the vaddr which would save you a clean up
step.

> +
> +	vaddr = base_vaddr + args->offset;
> +
> +	/* Assumes WC mapping */
> +	ret = wait_event_interruptible_timeout(
> +			gpu->event, *vaddr >= args->value, remaining_jiffies);

I feel like a barrier might be needed before checking *vaddr just in case you
get the interrupt and wake up the queue before the write posts from the
hardware.

> +

> +	if (ret == 0) {
> +		ret = -ETIMEDOUT;
> +		goto err_put_vaddr;
> +	} else if (ret == -ERESTARTSYS) {
> +		goto err_put_vaddr;
> +	}

You don't need either goto here because both paths execute the following cleanup
steps. I'm also not sure you need to worry about explicitly checking the
ERESTARTSYS value, I think that this would be sufficient:

 if (ret == 0)
     ret = -ETIMEDOUT;
 else if (ret > 0)
     ret = 0;

> +

Put your err_put_vaddr: label here, but looking up, if you move the bounds check
before the msm_gem_get_vaddr, I don't think you need a label.

> +	msm_gem_put_vaddr(obj);

Put the err_put_gem_object: label here.

> +	drm_gem_object_put_unlocked(obj);
> +	return 0;

return ret;

> +
> +err_put_vaddr:
> +	msm_gem_put_vaddr(obj);
> +err_put_gem_object:
> +	drm_gem_object_put_unlocked(obj);
> +	return ret;
> +}

And then these guys aren't needed.

> +
>  static const struct drm_ioctl_desc msm_ioctls[] = {
>  	DRM_IOCTL_DEF_DRV(MSM_GET_PARAM,    msm_ioctl_get_param,    DRM_RENDER_ALLOW),
>  	DRM_IOCTL_DEF_DRV(MSM_GEM_NEW,      msm_ioctl_gem_new,      DRM_RENDER_ALLOW),
> @@ -964,6 +1022,7 @@ static const struct drm_ioctl_desc msm_ioctls[] = {
>  	DRM_IOCTL_DEF_DRV(MSM_SUBMITQUEUE_NEW,   msm_ioctl_submitqueue_new,   DRM_RENDER_ALLOW),
>  	DRM_IOCTL_DEF_DRV(MSM_SUBMITQUEUE_CLOSE, msm_ioctl_submitqueue_close, DRM_RENDER_ALLOW),
>  	DRM_IOCTL_DEF_DRV(MSM_SUBMITQUEUE_QUERY, msm_ioctl_submitqueue_query, DRM_RENDER_ALLOW),
> +	DRM_IOCTL_DEF_DRV(MSM_WAIT_IOVA, msm_ioctl_wait_iova, DRM_RENDER_ALLOW),
>  };
>  
>  static const struct vm_operations_struct vm_ops = {
> diff --git a/include/uapi/drm/msm_drm.h b/include/uapi/drm/msm_drm.h
> index 0b85ed6a3710..8477f28a4ee1 100644
> --- a/include/uapi/drm/msm_drm.h
> +++ b/include/uapi/drm/msm_drm.h
> @@ -298,6 +298,17 @@ struct drm_msm_submitqueue_query {
>  	__u32 pad;
>  };
>  
> +/* This ioctl blocks until the u64 value at bo + offset is greater than or
> + * equal to the reference value.
> + */
> +struct drm_msm_wait_iova {
> +	__u32 handle;          /* in, GEM handle */
> +	__u32 pad;
> +	struct drm_msm_timespec timeout;   /* in */
> +	__u64 offset;          /* offset into bo */
> +	__u64 value;           /* reference value */

Any specific reason why we wouldn't just put the offset and value first and save
ourselves the padding?

> +};
> +
>  #define DRM_MSM_GET_PARAM              0x00
>  /* placeholder:
>  #define DRM_MSM_SET_PARAM              0x01
> @@ -315,6 +326,7 @@ struct drm_msm_submitqueue_query {
>  #define DRM_MSM_SUBMITQUEUE_NEW        0x0A
>  #define DRM_MSM_SUBMITQUEUE_CLOSE      0x0B
>  #define DRM_MSM_SUBMITQUEUE_QUERY      0x0C
> +#define DRM_MSM_WAIT_IOVA      0x0D
>  
>  #define DRM_IOCTL_MSM_GET_PARAM        DRM_IOWR(DRM_COMMAND_BASE + DRM_MSM_GET_PARAM, struct drm_msm_param)
>  #define DRM_IOCTL_MSM_GEM_NEW          DRM_IOWR(DRM_COMMAND_BASE + DRM_MSM_GEM_NEW, struct drm_msm_gem_new)
> @@ -327,6 +339,7 @@ struct drm_msm_submitqueue_query {
>  #define DRM_IOCTL_MSM_SUBMITQUEUE_NEW    DRM_IOWR(DRM_COMMAND_BASE + DRM_MSM_SUBMITQUEUE_NEW, struct drm_msm_submitqueue)
>  #define DRM_IOCTL_MSM_SUBMITQUEUE_CLOSE  DRM_IOW (DRM_COMMAND_BASE + DRM_MSM_SUBMITQUEUE_CLOSE, __u32)
>  #define DRM_IOCTL_MSM_SUBMITQUEUE_QUERY  DRM_IOW (DRM_COMMAND_BASE + DRM_MSM_SUBMITQUEUE_QUERY, struct drm_msm_submitqueue_query)
> +#define DRM_IOCTL_MSM_WAIT_IOVA        DRM_IOW (DRM_COMMAND_BASE + DRM_MSM_WAIT_IOVA, struct drm_msm_wait_iova)
>  
>  #if defined(__cplusplus)
>  }
> -- 
> 2.25.0.rc1.283.g88dfdc4193-goog
> 
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