> >> So in the case of write I/O using virtio-blk dataplane=off > >> [...] What is going to happen after the host there is > >> the real I/O completion, the host complete bh is executed? We go > >> through iothread to guest, in order to executte the > >> virtio-blk-complete request? > > > > How did the control transfer to QEMU user space (and which thread is > running vcpu or worker) > ->virtio_blk_device_realize > -> virtio_blk_req_complete > Was it the "real" interrupt for I/O completion from the device? > > Which qemu thread executes the code you mentioned?, vcpu or a > worker(iothread or main_loop) When did iothread finish its work? There are two ways: 1) the VCPU thread starts the I/O (control is transferred to QEMU user space by leaving KVM_RUN). The I/O system call happens in a worker thread. When the systemc call is finished the worker thread wakes up the I/O thread and the I/O thread executes virtio_blk_req_complete. 2) the VCPU thread (which is running KVM_RUN) writes to an eventfd, which wakes up the I/O thread. The I/O thread runs the I/O system call in a worker thread, same as case 1. Also like case 1, when the I/O is finished the worker thread wakes up the I/O thread and the I/O thread executes virtio_blk_req_complete. > I know that there are many exit reasons, but it's not clear to me > HOW exactly, transfer the control from the execution of one of these > instructions > to VMEXIT point which is "vmx_return: " _ASM_PTR " 2b \n\t" > Where does this extraction happened and we jumped to this label? > Is it inside of the corresponding ioctl implementation? > > I guess the answer is: "read the manual", which is fine to me, because > you already helped me a lot :) This is a more specific question, and thus easier to answer: after a vmexit the instruction pointer is reset to the VMCS's HOST_RIP field, and KVM writes the address of vmx_return to that field. :) Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
