Re: [PATCH RFC 4/5] vhost-vdpa: support IOTLB batching hints

[Jason Wang <jasowang@redhat.com>]

On 2020/6/28 下午5:58, Michael S. Tsirkin wrote:
> On Thu, Jun 18, 2020 at 01:56:25PM +0800, Jason Wang wrote:
>> This patches extend the vhost IOTLB API to accept batch updating hints
>> form userspace. When userspace wants update the device IOTLB in a
>> batch, it may do:
>>
>> 1) Write vhost_iotlb_msg with VHOST_IOTLB_BATCH_BEGIN flag
>> 2) Perform a batch of IOTLB updating via VHOST_IOTLB_UPDATE/INVALIDATE
>> 3) Write vhost_iotlb_msg with VHOST_IOTLB_BATCH_END flag
> As long as we are extending the interface,
> is there some way we could cut down the number of system calls needed
> here?


I'm not sure it's worth to do that since usually we only have less than 
10 regions.

A possible method is to carry multiple vhost_iotlb_message in one system 
call.


>
>
>> Vhost-vdpa may decide to batch the IOMMU/IOTLB updating in step 3 when
>> vDPA device support set_map() ops. This is useful for the vDPA device
>> that want to know all the mappings to tweak their own DMA translation
>> logic.
>>
>> For vDPA device that doesn't require set_map(), no behavior changes.
>>
>> This capability is advertised via VHOST_BACKEND_F_IOTLB_BATCH capability.
>>
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>> ---
>>   drivers/vhost/vdpa.c             | 30 +++++++++++++++++++++++-------
>>   include/uapi/linux/vhost.h       |  2 ++
>>   include/uapi/linux/vhost_types.h |  7 +++++++
>>   3 files changed, 32 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
>> index 453057421f80..8f624bbafee7 100644
>> --- a/drivers/vhost/vdpa.c
>> +++ b/drivers/vhost/vdpa.c
>> @@ -56,7 +56,9 @@ enum {
>>   };
>>   
>>   enum {
>> -	VHOST_VDPA_BACKEND_FEATURES = (1ULL << VHOST_BACKEND_F_IOTLB_MSG_V2)
>> +	VHOST_VDPA_BACKEND_FEATURES =
>> +	(1ULL << VHOST_BACKEND_F_IOTLB_MSG_V2) |
>> +	(1ULL << VHOST_BACKEND_F_IOTLB_BATCH),
>>   };
>>   
>>   /* Currently, only network backend w/o multiqueue is supported. */
>> @@ -77,6 +79,7 @@ struct vhost_vdpa {
>>   	int virtio_id;
>>   	int minor;
>>   	struct eventfd_ctx *config_ctx;
>> +	int in_batch;
>>   };
>>   
>>   static DEFINE_IDA(vhost_vdpa_ida);
>> @@ -125,6 +128,7 @@ static void vhost_vdpa_reset(struct vhost_vdpa *v)
>>   	const struct vdpa_config_ops *ops = vdpa->config;
>>   
>>   	ops->set_status(vdpa, 0);
>> +	v->in_batch = 0;
>>   }
>>   
>>   static long vhost_vdpa_get_device_id(struct vhost_vdpa *v, u8 __user *argp)
>> @@ -540,9 +544,10 @@ static int vhost_vdpa_map(struct vhost_vdpa *v,
>>   
>>   	if (ops->dma_map)
>>   		r = ops->dma_map(vdpa, iova, size, pa, perm);
>> -	else if (ops->set_map)
>> -		r = ops->set_map(vdpa, dev->iotlb);
>> -	else
>> +	else if (ops->set_map) {
>> +		if (!v->in_batch)
>> +			r = ops->set_map(vdpa, dev->iotlb);
>> +	} else
>>   		r = iommu_map(v->domain, iova, pa, size,
>>   			      perm_to_iommu_flags(perm));
>>   
>> @@ -559,9 +564,10 @@ static void vhost_vdpa_unmap(struct vhost_vdpa *v, u64 iova, u64 size)
>>   
>>   	if (ops->dma_map)
>>   		ops->dma_unmap(vdpa, iova, size);
>> -	else if (ops->set_map)
>> -		ops->set_map(vdpa, dev->iotlb);
>> -	else
>> +	else if (ops->set_map) {
>> +		if (!v->in_batch)
>> +			ops->set_map(vdpa, dev->iotlb);
>> +	} else
>>   		iommu_unmap(v->domain, iova, size);
>>   }
>>   
>> @@ -655,6 +661,8 @@ static int vhost_vdpa_process_iotlb_msg(struct vhost_dev *dev,
>>   					struct vhost_iotlb_msg *msg)
>>   {
>>   	struct vhost_vdpa *v = container_of(dev, struct vhost_vdpa, vdev);
>> +	struct vdpa_device *vdpa = v->vdpa;
>> +	const struct vdpa_config_ops *ops = vdpa->config;
>>   	int r = 0;
>>   
>>   	r = vhost_dev_check_owner(dev);
>> @@ -668,6 +676,14 @@ static int vhost_vdpa_process_iotlb_msg(struct vhost_dev *dev,
>>   	case VHOST_IOTLB_INVALIDATE:
>>   		vhost_vdpa_unmap(v, msg->iova, msg->size);
>>   		break;
>> +	case VHOST_IOTLB_BATCH_BEGIN:
>> +		v->in_batch = true;
>> +		break;
>> +	case VHOST_IOTLB_BATCH_END:
>> +		if (v->in_batch && ops->set_map)
>> +			ops->set_map(vdpa, dev->iotlb);
>> +		v->in_batch = false;
>> +		break;
>>   	default:
>>   		r = -EINVAL;
>>   		break;
>> diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
>> index 0c2349612e77..565da96f55d5 100644
>> --- a/include/uapi/linux/vhost.h
>> +++ b/include/uapi/linux/vhost.h
>> @@ -91,6 +91,8 @@
>>   
>>   /* Use message type V2 */
>>   #define VHOST_BACKEND_F_IOTLB_MSG_V2 0x1
>> +/* IOTLB can accpet batching hints */
> typo


Will fix.


>
>> +#define VHOST_BACKEND_F_IOTLB_BATCH  0x2
>>   
>>   #define VHOST_SET_BACKEND_FEATURES _IOW(VHOST_VIRTIO, 0x25, __u64)
>>   #define VHOST_GET_BACKEND_FEATURES _IOR(VHOST_VIRTIO, 0x26, __u64)
>> diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h
>> index 669457ce5c48..5c12faffdde9 100644
>> --- a/include/uapi/linux/vhost_types.h
>> +++ b/include/uapi/linux/vhost_types.h
>> @@ -60,6 +60,13 @@ struct vhost_iotlb_msg {
>>   #define VHOST_IOTLB_UPDATE         2
>>   #define VHOST_IOTLB_INVALIDATE     3
>>   #define VHOST_IOTLB_ACCESS_FAIL    4
>> +/* VHOST_IOTLB_BATCH_BEGIN is a hint that userspace will update
>> + * several mappings afterwards. VHOST_IOTLB_BATCH_END is a hint that
>> + * userspace had finished the mapping updating.
>
> Well not just hints - in fact updates do not take place
> until _END.
>
> How about:
>
> /* VHOST_IOTLB_BATCH_BEGIN and VHOST_IOTLB_BATCH_END allow modifying
>   * multiple mappings in one go: beginning with
>   * VHOST_IOTLB_BATCH_BEGIN, followed by any number of
>     VHOST_IOTLB_UPDATE messages, and ending with VHOST_IOTLB_BATCH_END.
>   */


That's better.


>
>
>> When those two flags
>> + * were set, kernel will ignore the rest fileds of the IOTLB message.
> how about:
>
> when one of these two values is used as the message type, the
> rest of the fields in the message are ignored.


Yes.

Will fix.

Thanks


>
>> + */
>> +#define VHOST_IOTLB_BATCH_BEGIN    5
>> +#define VHOST_IOTLB_BATCH_END      6
>>   	__u8 type;
>>   };
>>   
>> -- 
>> 2.20.1