RE: [PATCH v6 6/6] drm/i915/gvt: Adding interface so user space can get the dma-buf

["Chen, Xiaoguang" <xiaoguang.chen@intel.com>]

Hi Alex,

>-----Original Message-----
>From: Alex Williamson [mailto:alex.williamson@redhat.com]
>Sent: Friday, June 02, 2017 2:08 AM
>To: Chen, Xiaoguang <xiaoguang.chen@intel.com>
>Cc: kraxel@redhat.com; chris@chris-wilson.co.uk; intel-
>gfx@lists.freedesktop.org; linux-kernel@vger.kernel.org;
>zhenyuw@linux.intel.com; Lv, Zhiyuan <zhiyuan.lv@intel.com>; intel-gvt-
>dev@lists.freedesktop.org; Wang, Zhi A <zhi.a.wang@intel.com>; Tian, Kevin
><kevin.tian@intel.com>
>Subject: Re: [PATCH v6 6/6] drm/i915/gvt: Adding interface so user space can get
>the dma-buf
>
>On Sat, 27 May 2017 16:38:52 +0800
>Xiaoguang Chen <xiaoguang.chen@intel.com> wrote:
>
>> User space should create the management fd for the dma-buf operation first.
>> Then user can query the plane information and create dma-buf if
>> necessary using the management fd.
>>
>> Signed-off-by: Xiaoguang Chen <xiaoguang.chen@intel.com>
>> ---
>>  drivers/gpu/drm/i915/gvt/dmabuf.c |  12 ++++
>>  drivers/gpu/drm/i915/gvt/dmabuf.h |   5 ++
>>  drivers/gpu/drm/i915/gvt/gvt.c    |   2 +
>>  drivers/gpu/drm/i915/gvt/gvt.h    |   5 ++
>>  drivers/gpu/drm/i915/gvt/kvmgt.c  | 144
>++++++++++++++++++++++++++++++++++++++
>>  drivers/gpu/drm/i915/gvt/vgpu.c   |   1 +
>>  6 files changed, 169 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/gvt/dmabuf.c
>> b/drivers/gpu/drm/i915/gvt/dmabuf.c
>> index c831e91..9759e9a 100644
>> --- a/drivers/gpu/drm/i915/gvt/dmabuf.c
>> +++ b/drivers/gpu/drm/i915/gvt/dmabuf.c
>> @@ -226,6 +226,7 @@ int intel_vgpu_create_dmabuf(struct intel_vgpu *vgpu,
>void *args)
>>  	struct vfio_vgpu_dmabuf_info *gvt_dmabuf = args;
>>  	struct intel_vgpu_fb_info *fb_info;
>>  	int ret;
>> +	struct intel_vgpu_dmabuf_obj *dmabuf_obj;
>>
>>  	ret = intel_vgpu_get_plane_info(dev, vgpu, &gvt_dmabuf->plane_info);
>>  	if (ret != 0)
>> @@ -263,6 +264,17 @@ int intel_vgpu_create_dmabuf(struct intel_vgpu *vgpu,
>void *args)
>>  		gvt_vgpu_err("create dma-buf fd failed ret:%d\n", ret);
>>  		return ret;
>>  	}
>> +	dmabuf_obj = kmalloc(sizeof(*dmabuf_obj), GFP_KERNEL);
>> +	if (dmabuf_obj == NULL) {
>> +		kfree(fb_info);
>> +		i915_gem_object_put(obj);
>> +		gvt_vgpu_err("alloc dmabuf_obj failed\n");
>> +		return -ENOMEM;
>> +	}
>> +	dmabuf_obj->obj = obj;
>> +	INIT_LIST_HEAD(&dmabuf_obj->list);
>> +	list_add_tail(&dmabuf_obj->list, &vgpu->dmabuf_obj_list_head);
>> +
>>  	gvt_dmabuf->fd = ret;
>>
>>  	return 0;
>> diff --git a/drivers/gpu/drm/i915/gvt/dmabuf.h
>> b/drivers/gpu/drm/i915/gvt/dmabuf.h
>> index 8be9979..cafa781 100644
>> --- a/drivers/gpu/drm/i915/gvt/dmabuf.h
>> +++ b/drivers/gpu/drm/i915/gvt/dmabuf.h
>> @@ -31,6 +31,11 @@ struct intel_vgpu_fb_info {
>>  	uint32_t fb_size;
>>  };
>>
>> +struct intel_vgpu_dmabuf_obj {
>> +	struct drm_i915_gem_object *obj;
>> +	struct list_head list;
>> +};
>> +
>>  int intel_vgpu_query_plane(struct intel_vgpu *vgpu, void *args);  int
>> intel_vgpu_create_dmabuf(struct intel_vgpu *vgpu, void *args);
>>
>> diff --git a/drivers/gpu/drm/i915/gvt/gvt.c
>> b/drivers/gpu/drm/i915/gvt/gvt.c index 2032917..dbc3f86 100644
>> --- a/drivers/gpu/drm/i915/gvt/gvt.c
>> +++ b/drivers/gpu/drm/i915/gvt/gvt.c
>> @@ -54,6 +54,8 @@ static const struct intel_gvt_ops intel_gvt_ops = {
>>  	.vgpu_reset = intel_gvt_reset_vgpu,
>>  	.vgpu_activate = intel_gvt_activate_vgpu,
>>  	.vgpu_deactivate = intel_gvt_deactivate_vgpu,
>> +	.vgpu_query_plane = intel_vgpu_query_plane,
>> +	.vgpu_create_dmabuf = intel_vgpu_create_dmabuf,
>>  };
>>
>>  /**
>> diff --git a/drivers/gpu/drm/i915/gvt/gvt.h
>> b/drivers/gpu/drm/i915/gvt/gvt.h index 763a8c5..a855797 100644
>> --- a/drivers/gpu/drm/i915/gvt/gvt.h
>> +++ b/drivers/gpu/drm/i915/gvt/gvt.h
>> @@ -185,8 +185,11 @@ struct intel_vgpu {
>>  		struct kvm *kvm;
>>  		struct work_struct release_work;
>>  		atomic_t released;
>> +		struct vfio_device *vfio_device;
>>  	} vdev;
>>  #endif
>> +	int dmabuf_mgr_fd;
>> +	struct list_head dmabuf_obj_list_head;
>>  };
>>
>>  struct intel_gvt_gm {
>> @@ -467,6 +470,8 @@ struct intel_gvt_ops {
>>  	void (*vgpu_reset)(struct intel_vgpu *);
>>  	void (*vgpu_activate)(struct intel_vgpu *);
>>  	void (*vgpu_deactivate)(struct intel_vgpu *);
>> +	int (*vgpu_query_plane)(struct intel_vgpu *vgpu, void *);
>> +	int (*vgpu_create_dmabuf)(struct intel_vgpu *vgpu, void *);
>>  };
>>
>>
>> diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c
>> b/drivers/gpu/drm/i915/gvt/kvmgt.c
>> index 389f072..a079080 100644
>> --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
>> +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
>> @@ -41,6 +41,7 @@
>>  #include <linux/kvm_host.h>
>>  #include <linux/vfio.h>
>>  #include <linux/mdev.h>
>> +#include <linux/anon_inodes.h>
>>
>>  #include "i915_drv.h"
>>  #include "gvt.h"
>> @@ -524,6 +525,125 @@ static int intel_vgpu_reg_init_opregion(struct
>intel_vgpu *vgpu)
>>  	return ret;
>>  }
>>
>> +static int kvmgt_get_vfio_device(struct intel_vgpu *vgpu) {
>> +	struct vfio_device *device;
>> +
>> +	device = vfio_device_get_from_dev(mdev_dev(vgpu->vdev.mdev));
>> +	if (device == NULL)
>> +		return -ENODEV;
>> +	vgpu->vdev.vfio_device = device;
>> +
>> +	return 0;
>> +}
>> +
>> +static void kvmgt_put_vfio_device(struct intel_vgpu *vgpu) {
>> +	vfio_device_put(vgpu->vdev.vfio_device);
>> +}
>> +
>> +static int intel_vgpu_dmabuf_mgr_fd_mmap(struct file *file,
>> +		struct vm_area_struct *vma)
>> +{
>> +	return -EPERM;
>> +}
>> +
>> +static int intel_vgpu_dmabuf_mgr_fd_release(struct inode *inode,
>> +		struct file *filp)
>> +{
>> +	struct intel_vgpu *vgpu = filp->private_data;
>> +	struct intel_vgpu_dmabuf_obj *obj;
>> +	struct list_head *pos;
>> +
>> +	if (WARN_ON(!vgpu->vdev.vfio_device))
>> +		return -ENODEV;
>> +
>> +	list_for_each(pos, &vgpu->dmabuf_obj_list_head) {
>> +		obj = container_of(pos, struct intel_vgpu_dmabuf_obj, list);
>> +		if (WARN_ON(!obj))
>> +			return -ENODEV;
>> +		kfree(obj->obj->gvt_info);
>> +		i915_gem_object_put(obj->obj);
>> +		kfree(obj);
>> +		kvmgt_put_vfio_device(vgpu);
>
>Can we do this?  If I understand, we're releasing all the references and allocations
>for the dmabuf fds on release of the manager fd.  What happens if the user
>continues trying to access those dmabuf fds after this?
I think we can do this here.
The dma-buf's release function dma_buf_release() will be called by kernel which means all the created dmabufs will be invalid even we do not release all the references and allocations here.

>
>> +	}
>> +	kvmgt_put_vfio_device(vgpu);
>> +
>> +	return 0;
>> +}
>> +
>> +static long intel_vgpu_dmabuf_mgr_fd_ioctl(struct file *filp,
>> +		unsigned int ioctl, unsigned long arg) {
>> +	struct intel_vgpu *vgpu = filp->private_data;
>> +	int minsz;
>> +	int ret;
>> +	struct fd f;
>> +
>> +	f = fdget(vgpu->dmabuf_mgr_fd);
>> +	if (!f.file)
>> +		return -EBADF;
>> +
>> +	if (ioctl == VFIO_DEVICE_QUERY_PLANE) {
>> +		struct vfio_vgpu_plane_info info;
>> +
>> +		minsz = offsetofend(struct vfio_vgpu_plane_info, resv);
>> +		if (copy_from_user(&info, (void __user *)arg, minsz)) {
>> +			fdput(f);
>> +			return -EFAULT;
>> +		}
>> +		if (info.argsz < minsz) {
>> +			fdput(f);
>> +			return -EINVAL;
>> +		}
>> +		ret = intel_gvt_ops->vgpu_query_plane(vgpu, &info);
>> +		if (ret != 0) {
>> +			fdput(f);
>> +			gvt_vgpu_err("query plane failed:%d\n", ret);
>> +			return -EINVAL;
>> +		}
>> +		fdput(f);
>> +		return copy_to_user((void __user *)arg, &info, minsz) ?
>> +								-EFAULT : 0;
>> +	} else if (ioctl == VFIO_DEVICE_CREATE_DMABUF) {
>> +		struct vfio_vgpu_dmabuf_info dmabuf;
>> +
>> +		minsz = offsetofend(struct vfio_vgpu_dmabuf_info, resv);
>> +		if (copy_from_user(&dmabuf, (void __user *)arg, minsz)) {
>> +			fdput(f);
>> +			return -EFAULT;
>> +		}
>> +		if (dmabuf.argsz < minsz) {
>> +			fdput(f);
>> +			return -EINVAL;
>> +		}
>> +		ret = kvmgt_get_vfio_device(vgpu);
>> +		if (ret != 0)
>> +			return ret;
>
>Missed an fdput, though I'm not sure I understand the value of the original fdget
>or the dmabuf_mgr_fd field at all.  dmabuf_mgr_fd is only used here, presumably
>to add a reference to the fd while we're in the ioctl, but we're in the ioctl function
>of that fd, so I think there are already references elsewhere.
Make sense. Fdget/fdput can be removed.

>
>> +
>> +		ret = intel_gvt_ops->vgpu_create_dmabuf(vgpu, &dmabuf);
>> +		if (ret != 0) {
>> +			kvmgt_put_vfio_device(vgpu);
>> +			fdput(f);
>> +			return -EINVAL;
>
>Why not return the errno that vgpu_create_dmabuf provided?
Will change to use the returned errno.

>
>> +		}
>> +		fdput(f);
>> +		return copy_to_user((void __user *)arg, &dmabuf, minsz) ?
>> +								-EFAULT : 0;
>> +	}
>> +
>> +	fdput(f);
>> +	gvt_vgpu_err("unsupported dmabuf operation\n");
>> +
>> +	return -EINVAL;
>> +}
>> +
>> +static const struct file_operations intel_vgpu_dmabuf_mgr_fd_ops = {
>> +	.release        = intel_vgpu_dmabuf_mgr_fd_release,
>> +	.unlocked_ioctl = intel_vgpu_dmabuf_mgr_fd_ioctl,
>> +	.mmap           = intel_vgpu_dmabuf_mgr_fd_mmap,
>> +	.llseek         = noop_llseek,
>> +};
>>  static int intel_vgpu_create(struct kobject *kobj, struct mdev_device
>> *mdev)  {
>>  	struct intel_vgpu *vgpu = NULL;
>> @@ -1259,6 +1379,30 @@ static long intel_vgpu_ioctl(struct mdev_device
>*mdev, unsigned int cmd,
>>  	} else if (cmd == VFIO_DEVICE_RESET) {
>>  		intel_gvt_ops->vgpu_reset(vgpu);
>>  		return 0;
>> +	} else if (cmd == VFIO_DEVICE_GET_FD) {
>> +		int fd;
>> +		u32 type;
>> +		int ret;
>> +
>> +		if (copy_from_user(&type, (void __user *)arg, sizeof(type)))
>> +			return -EINVAL;
>> +		if (type != VFIO_DEVICE_DMABUF_MGR_FD)
>> +			return -EINVAL;
>> +
>> +		ret = kvmgt_get_vfio_device(vgpu);
>> +		if (ret != 0)
>> +			return ret;
>> +
>> +		fd = anon_inode_getfd("intel-vgpu-dmabuf-mgr-fd",
>> +			&intel_vgpu_dmabuf_mgr_fd_ops,
>> +			vgpu, O_RDWR | O_CLOEXEC);
>> +		if (fd < 0) {
>> +			gvt_vgpu_err("create dmabuf mgr fd failed\n");
>> +			return -EINVAL;
>
>Error path leaks vfio_device reference.
Will correct in the next version.

>
>> +		}
>> +		vgpu->dmabuf_mgr_fd = fd;
>
>As above, unclear value of this field, additionally, what if the user calls
>VFIO_DEVICE_GET_FD more than once?
Ah, good question.
VFIO_DEVICE_GET_FD should only be called once.
And we should add a check if the vgpu->dmabuf_mgr_fd is not 0 which means VFIO_DEVICE_GET_FD had been called before we should return an error.

>
>> +
>> +		return fd;
>>  	}
>>
>>  	return 0;
>> diff --git a/drivers/gpu/drm/i915/gvt/vgpu.c
>> b/drivers/gpu/drm/i915/gvt/vgpu.c index 6e3cbd8..af6fc74 100644
>> --- a/drivers/gpu/drm/i915/gvt/vgpu.c
>> +++ b/drivers/gpu/drm/i915/gvt/vgpu.c
>> @@ -346,6 +346,7 @@ static struct intel_vgpu
>*__intel_gvt_create_vgpu(struct intel_gvt *gvt,
>>  	vgpu->gvt = gvt;
>>  	vgpu->sched_ctl.weight = param->weight;
>>  	bitmap_zero(vgpu->tlb_handle_pending, I915_NUM_ENGINES);
>> +	INIT_LIST_HEAD(&vgpu->dmabuf_obj_list_head);
>>
>>  	intel_vgpu_init_cfg_space(vgpu, param->primary);
>>