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SubjectRe: [PATCH 2/2 v4] vfio-cdx: add ioctl support for bus master enable
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On 7/26/2023 4:55 PM, Greg KH wrote:
> On Wed, Jul 26, 2023 at 04:32:20PM +0530, Nipun Gupta wrote:
>> add VFIO_DEVICE_CDX_CTRL IOCTL to expose control operations for CDX
>> devices to VFIO users. Support Bus master enable and Bus master disable
>> on CDX bus control.
>>
>> Signed-off-by: Shubham Rohila <shubham.rohila@amd.com>
>> Signed-off-by: Nipun Gupta <nipun.gupta@amd.com>
>
> Who wrote this? The signed-off-by ordering seems odd.
>
>
>> ---
>>
>> Changes in v4:
>> - This patch is newly added which uses cdx_set_master() and
>> cdx_clear_master() APIs.
>>
>> drivers/vfio/cdx/main.c | 26 ++++++++++++++++++++++++++
>> include/uapi/linux/vfio.h | 14 ++++++++++++++
>> 2 files changed, 40 insertions(+)
>>
>> diff --git a/drivers/vfio/cdx/main.c b/drivers/vfio/cdx/main.c
>> index c376a69d2db2..c39a965716f4 100644
>> --- a/drivers/vfio/cdx/main.c
>> +++ b/drivers/vfio/cdx/main.c
>> @@ -98,6 +98,30 @@ static int vfio_cdx_ioctl_get_region_info(struct vfio_cdx_device *vdev,
>> return copy_to_user(arg, &info, minsz) ? -EFAULT : 0;
>> }
>>
>> +static int vfio_cdx_ioctl_ctrl(struct vfio_cdx_device *vdev,
>> + struct vfio_device_cdx_ctrl __user *arg)
>> +{
>> + unsigned long minsz = offsetofend(struct vfio_device_cdx_ctrl, op);
>> + struct cdx_device *cdx_dev = to_cdx_device(vdev->vdev.dev);
>> + struct vfio_device_cdx_ctrl ops;
>> +
>> + if (copy_from_user(&ops, arg, minsz))
>> + return -EFAULT;
>> +
>> + if (ops.argsz < minsz)
>> + return -EINVAL;
>> +
>> + switch (ops.op) {
>> + case VFIO_CDX_CTRL_CLEAR_MASTER:
>> + cdx_clear_master(cdx_dev);
>> + return 0;
>> + case VFIO_CDX_CTRL_SET_MASTER:
>> + return cdx_set_master(cdx_dev);
>> + default:
>> + return -EINVAL;
>> + }
>> +}
>> +
>> static long vfio_cdx_ioctl(struct vfio_device *core_vdev,
>> unsigned int cmd, unsigned long arg)
>> {
>> @@ -112,6 +136,8 @@ static long vfio_cdx_ioctl(struct vfio_device *core_vdev,
>> return vfio_cdx_ioctl_get_region_info(vdev, uarg);
>> case VFIO_DEVICE_RESET:
>> return cdx_dev_reset(core_vdev->dev);
>> + case VFIO_DEVICE_CDX_CTRL:
>> + return vfio_cdx_ioctl_ctrl(vdev, uarg);
>> default:
>> return -ENOTTY;
>> }
>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
>> index 20c804bdc09c..5f6a58f9f8e2 100644
>> --- a/include/uapi/linux/vfio.h
>> +++ b/include/uapi/linux/vfio.h
>> @@ -1649,6 +1649,20 @@ struct vfio_iommu_spapr_tce_remove {
>> };
>> #define VFIO_IOMMU_SPAPR_TCE_REMOVE _IO(VFIO_TYPE, VFIO_BASE + 20)
>>
>> +/**
>> + * VFIO_DEVICE_CDX_CTRL - _IO(VFIO_TYPE, VFIO_BASE + 21)
>> + *
>> + * Control CDX device.
>> + * Variable op is set as per the operation required
>
> But what is argsz set to?

This is required to be set as size of the data being passed; which in
this case is sizeof(struct vfio_device_cdx_ctrl).

>
>> + */
>> +struct vfio_device_cdx_ctrl {
>> + __u32 argsz;
>> + __u32 op;
>> +#define VFIO_CDX_CTRL_SET_MASTER 0 /* Set Bus Master */
>> +#define VFIO_CDX_CTRL_CLEAR_MASTER 1 /* Clear Bus Master */
>> +};
>> +#define VFIO_DEVICE_CDX_CTRL _IO(VFIO_TYPE, VFIO_BASE + 21)
>> +
>
> Doesn't vfio stuff require a spec and agreement on the interface
> somewhere? Has that happened here already?

As suggested by Alex, we can use VFIO_DEVICE_FEATURE which seems well
suited here.

>
> And why an ioctl? Why would userspace care about this type of control?

CDX devices are by default in bus master disabled state and user-space
drivers will set the bus mastering once appropriate IOMMU mappings have
been set-up.

Thanks,
Nipun

>
> thanks,
>
> greg k-h

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