Re: [PATCH v12 rdma-next 4/8] RDMA/efa: Use the common mmap_xa helpers

[Gal Pressman <galpress@amazon.com>]

On 05/11/2019 21:54, Jason Gunthorpe wrote:
>>  static int qp_mmap_entries_setup(struct efa_qp *qp,
>>  				 struct efa_dev *dev,
>>  				 struct efa_ucontext *ucontext,
>>  				 struct efa_com_create_qp_params *params,
>>  				 struct efa_ibv_create_qp_resp *resp)
>>  {
>> -	/*
>> -	 * Once an entry is inserted it might be mmapped, hence cannot be
>> -	 * cleaned up until dealloc_ucontext.
>> -	 */
>> -	resp->sq_db_mmap_key =
>> -		mmap_entry_insert(dev, ucontext, qp,
>> -				  dev->db_bar_addr + resp->sq_db_offset,
>> -				  PAGE_SIZE, EFA_MMAP_IO_NC);
>> -	if (resp->sq_db_mmap_key == EFA_MMAP_INVALID)
>> +	size_t length;
>> +	u64 address;
>> +
>> +	address = dev->db_bar_addr + resp->sq_db_offset;
>> +	qp->sq_db_mmap_entry =
>> +		efa_user_mmap_entry_insert(&ucontext->ibucontext,
>> +					   address,
>> +					   PAGE_SIZE, EFA_MMAP_IO_NC,
>> +					   &resp->sq_db_mmap_key);
> 
> I'm still confused how this is OK for the lifetime, 'sq_db_offset'
> comes from the device, does the device prevent re-use of the same
> db_offset until the ucontext is closed? If so that deserves a comment
> in here.

The device prevents reuse of the DB offset until the UAR is deallocated (during
ucontext close). Same applies for the RQ DB and LLQ offset.