Re: [PATCH v8 3/6] drm/xe/uapi: Define drm_xe_vm_get_property

[Jianxun Zhang <jianxun.zhang@intel.com>]

On 3/13/25 11:34, Jonathan Cavitt wrote:
> Add initial declarations for the drm_xe_vm_get_property ioctl.
> 
> Signed-off-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
> ---
>   include/uapi/drm/xe_drm.h | 69 +++++++++++++++++++++++++++++++++++++++
>   1 file changed, 69 insertions(+)
> 
> diff --git a/include/uapi/drm/xe_drm.h b/include/uapi/drm/xe_drm.h
> index 616916985e3f..0ed52666b4e9 100644
> --- a/include/uapi/drm/xe_drm.h
> +++ b/include/uapi/drm/xe_drm.h
> @@ -81,6 +81,7 @@ extern "C" {
>    *  - &DRM_IOCTL_XE_EXEC
>    *  - &DRM_IOCTL_XE_WAIT_USER_FENCE
>    *  - &DRM_IOCTL_XE_OBSERVATION
> + *  - &DRM_IOCTL_XE_VM_GET_PROPERTY
>    */
>   
>   /*
> @@ -102,6 +103,7 @@ extern "C" {
>   #define DRM_XE_EXEC			0x09
>   #define DRM_XE_WAIT_USER_FENCE		0x0a
>   #define DRM_XE_OBSERVATION		0x0b
> +#define DRM_XE_VM_GET_PROPERTY		0x0c
>   
>   /* Must be kept compact -- no holes */
>   
> @@ -117,6 +119,7 @@ extern "C" {
>   #define DRM_IOCTL_XE_EXEC			DRM_IOW(DRM_COMMAND_BASE + DRM_XE_EXEC, struct drm_xe_exec)
>   #define DRM_IOCTL_XE_WAIT_USER_FENCE		DRM_IOWR(DRM_COMMAND_BASE + DRM_XE_WAIT_USER_FENCE, struct drm_xe_wait_user_fence)
>   #define DRM_IOCTL_XE_OBSERVATION		DRM_IOW(DRM_COMMAND_BASE + DRM_XE_OBSERVATION, struct drm_xe_observation_param)
> +#define DRM_IOCTL_XE_VM_GET_PROPERTY	DRM_IOWR(DRM_COMMAND_BASE + DRM_XE_VM_GET_PROPERTY, struct drm_xe_vm_get_property)
>   
>   /**
>    * DOC: Xe IOCTL Extensions
> @@ -1189,6 +1192,72 @@ struct drm_xe_vm_bind {
>   	__u64 reserved[2];
>   };
>   
> +/** struct xe_vm_fault - Describes faults for %DRM_XE_VM_GET_PROPERTY_FAULTS */
> +struct xe_vm_fault {
> +	/** @address: Address of the fault */
> +	__u64 address;
> +#define DRM_XE_FAULT_ADDRESS_TYPE_NONE_EXT		0
> +#define DRM_XE_FAULT_ADDRESS_TYPE_READ_INVALID_EXT	1
> +#define DRM_XE_FAULT_ADDRESS_TYPE_WRITE_INVALID_EXT	2
> +	/** @address_type: Type of address access that resulted in fault */
> +	__u32 address_type;
> +	/** @address_precision: Precision of faulted address */
> +	__u32 address_precision;
> +	/** @fault_level: fault level of the fault */
> +	__u8 fault_level;
> +	/** @engine_class: class of engine fault was reported on */
> +	__u8 engine_class;
> +	/** @engine_instance: instance of engine fault was reported on */
> +	__u8 engine_instance;
> +	/** @pad: MBZ */
> +	__u8 pad[5];
> +	/** @reserved: MBZ */
> +	__u64 reserved[3];
> +};
> +
> +/**
> + * struct drm_xe_vm_get_property - Input of &DRM_IOCTL_XE_VM_GET_PROPERTY
> + *
> + * The user provides a VM ID and a property to query for.  The ioctl will return
> + * the size of the data expected to be returned in @size.  Performing the query
> + * again with memory allocated to @data of size @size will return the requested
> + * data to the allocated memory.
> + *
> + * Some get property requests may be scalar values and require no memory allocation.
> + * In such cases, the first call to this ioctl will not set @size and will return
> + * the requested value to @value instead.
A kernel driver cannot assume user space always plays nicely (two calls 
in the expected order). Instead, the design should be able to deal with 
all possibilities.

I suggest rewording this comment from another angle for two different 
behaviors. Something like "caller passes size with zero, ioctl returns 
actual size of a property only; caller passes a non-zero size, ioctl returns
error if size < prop's size, otherwise the size of prop and fills the 
data in memory"

In this way, the usage doesn't rely on the order of calls from user space.
> + *
> + * The @property can be:
> + *  - %DRM_XE_VM_GET_PROPERTY_FAULTS
> + */
> +struct drm_xe_vm_get_property {
> +	/** @extensions: Pointer to the first extension struct, if any */
> +	__u64 extensions;
> +
> +	/** @vm_id: The ID of the VM to query the properties of */
> +	__u32 vm_id;
> +
> +#define DRM_XE_VM_GET_PROPERTY_FAULTS		0
> +	/** @property: property to get */
> +	__u32 property;
> +
> +	/** @size: Size to allocate for @data */
> +	__u32 size;
> +
> +	/** @pad: MBZ */
> +	__u32 pad;
> +
> +	union {
> +		/** @data: Pointer to user-defined array of flexible size and type */
> +		__u64 data;
> +		/** @value: Return value for scalar queries */
> +		__u64 value;
> +	};
> +
> +	/** @reserved: MBZ */
> +	__u64 reserved[3];
> +};
> +
>   /**
>    * struct drm_xe_exec_queue_create - Input of &DRM_IOCTL_XE_EXEC_QUEUE_CREATE
>    *