1.. SPDX-License-Identifier: GPL-2.0 2 3I/O request handling 4==================== 5 6An I/O request of a User VM, which is constructed by the hypervisor, is 7distributed by the ACRN Hypervisor Service Module to an I/O client 8corresponding to the address range of the I/O request. Details of I/O request 9handling are described in the following sections. 10 111. I/O request 12-------------- 13 14For each User VM, there is a shared 4-KByte memory region used for I/O requests 15communication between the hypervisor and Service VM. An I/O request is a 16256-byte structure buffer, which is 'struct acrn_io_request', that is filled by 17an I/O handler of the hypervisor when a trapped I/O access happens in a User 18VM. ACRN userspace in the Service VM first allocates a 4-KByte page and passes 19the GPA (Guest Physical Address) of the buffer to the hypervisor. The buffer is 20used as an array of 16 I/O request slots with each I/O request slot being 256 21bytes. This array is indexed by vCPU ID. 22 232. I/O clients 24-------------- 25 26An I/O client is responsible for handling User VM I/O requests whose accessed 27GPA falls in a certain range. Multiple I/O clients can be associated with each 28User VM. There is a special client associated with each User VM, called the 29default client, that handles all I/O requests that do not fit into the range of 30any other clients. The ACRN userspace acts as the default client for each User 31VM. 32 33Below illustration shows the relationship between I/O requests shared buffer, 34I/O requests and I/O clients. 35 36:: 37 38 +------------------------------------------------------+ 39 | Service VM | 40 |+--------------------------------------------------+ | 41 || +----------------------------------------+ | | 42 || | shared page ACRN userspace | | | 43 || | +-----------------+ +------------+ | | | 44 || +----+->| acrn_io_request |<-+ default | | | | 45 || | | | +-----------------+ | I/O client | | | | 46 || | | | | ... | +------------+ | | | 47 || | | | +-----------------+ | | | 48 || | +-|--------------------------------------+ | | 49 ||---|----|-----------------------------------------| | 50 || | | kernel | | 51 || | | +----------------------+ | | 52 || | | | +-------------+ HSM | | | 53 || | +--------------+ | | | | 54 || | | | I/O clients | | | | 55 || | | | | | | | 56 || | | +-------------+ | | | 57 || | +----------------------+ | | 58 |+---|----------------------------------------------+ | 59 +----|-------------------------------------------------+ 60 | 61 +----|-------------------------------------------------+ 62 | +-+-----------+ | 63 | | I/O handler | ACRN Hypervisor | 64 | +-------------+ | 65 +------------------------------------------------------+ 66 673. I/O request state transition 68------------------------------- 69 70The state transitions of an ACRN I/O request are as follows. 71 72:: 73 74 FREE -> PENDING -> PROCESSING -> COMPLETE -> FREE -> ... 75 76- FREE: this I/O request slot is empty 77- PENDING: a valid I/O request is pending in this slot 78- PROCESSING: the I/O request is being processed 79- COMPLETE: the I/O request has been processed 80 81An I/O request in COMPLETE or FREE state is owned by the hypervisor. HSM and 82ACRN userspace are in charge of processing the others. 83 844. Processing flow of I/O requests 85---------------------------------- 86 87a. The I/O handler of the hypervisor will fill an I/O request with PENDING 88 state when a trapped I/O access happens in a User VM. 89b. The hypervisor makes an upcall, which is a notification interrupt, to 90 the Service VM. 91c. The upcall handler schedules a worker to dispatch I/O requests. 92d. The worker looks for the PENDING I/O requests, assigns them to different 93 registered clients based on the address of the I/O accesses, updates 94 their state to PROCESSING, and notifies the corresponding client to handle. 95e. The notified client handles the assigned I/O requests. 96f. The HSM updates I/O requests states to COMPLETE and notifies the hypervisor 97 of the completion via hypercalls. 98