Hi Folks, Background ========== Some days ago, we had a discussion on the topic of channel path virtualization. Ref: Subject: [PATCH 0/3] Channel Path realted CRW generation Message-Id: <20170727015418.85407-1-bjsdjshi@xxxxxxxxxxxxxxxxxx> URL: https://lists.nongnu.org/archive/html/qemu-devel/2017-07/msg08414.html Indeed that thread is not short and discussed many aspects in a non-concentrated manner. The parts those are most valuable to me are: 1. a re-modelling for channel path is surely the best offer, but is not possible to have in the near future. 2. to enhance the path related functionalities, using PNO and PNOM might be something we can do for now. This may be something that I could improve without model related arguments. So here I have this series targeting to add basic channel path event handling for vfio-ccw -- no touch of the channel path modelling in both the kernel and the QEMU side, but find a way to sync path status change to guest lazily using SCSW_FLAGS_MASK_PNO and pmcw->pnom. In short, I want to enhance path related stuff (to be more specific: sync up path status to the guest) on a best effort basis, which means in a way that won't get us invloed to do channel path re-modelling. What benifit can we get from this? The administrator of a virtual machine can get uptodate (in some extent) status of the current using channel paths, so he/she can monitor paths status and get path problem noticed timely (see the example below). I think we can start a new round discussion based on this series. So reviewers can give their comments based on some code, and then we can decide if this is we want or not. As flagged with RFC, the intention of this series is to show what I have for now, and what could the code look like in general. Thus I can get some early feedbacks. I would expect to see opinions on: - is the target (mentioned above) of this series welcomed or not. - is the approach of this series good or bad. So I can either move on with this (or with other suggested approach) or leave it alone. Basic Introduction of The Patches ================================= This is the kernel counterpart, which mainly does: 1. add a schib vfio region for userland to _store_ subchannel information. 2. add a channel path vfio irq to notify userland with chp status change event. 3. add .chp_event handler for vfio-ccw driver, so the driver handles chp event, and signals userland about the event. With the above work, userland can be signaled with chp related event, and then it can read out uptodate SCHIB from the new region, and sync up path related information to the corresponding virtual subchannel. So a guest can sense the path update in some extent. For the QEMU counterpart, please ref: [RFC PATCH 0/5] vfio/ccw: basic channel path event handling The QEMU counterpart mainly does: 1. add handling of the schib region, so that it can read out the newest schib information. 2. add handling of the chp irq, so that it can get notification of channel path status change. 3. once there is a chp status event, synchronize related information from the newest schib information to guest lazily. What are still missing, thus need to be offered in the next version are: - I/O termination and FSM state handling if currently we have I/O on the status switched path. - Vary on/off event is not sensible to a guest. Example ======= With both the kernel and Qemu parts applied, we can notice some new behaviors of a channel path when we have a guest with a passed through vfio-ccw device using it. The guest can reflect the chp status change of the host side lazily, and synchronize the updated information. For example: 0. Prepare a vfio subchannel on the host: [root@host ~]# lscss --vfio 013f MDEV Subchan. PIM PAM POM CHPIDs ------------------------------------------------------------------------------ 6dfd3ec5-e8b3-4e18-a6fe-57bc9eceb920 0.0.013f f0 f0 ff 42434445 00000000 1. Pass-through subchannel 0.0.013f to a guest: -device vfio-ccw,sysfsdev="$MDEV_FILE_PATH",devno=0.0.3f3f 2. Start the guest and check the device and path information: [root@guest ~]# lscss 0002 Device Subchan. DevType CU Type Use PIM PAM POM CHPIDs ---------------------------------------------------------------------- 0.0.3f3f 0.0.0002 3390/0c 3990/e9 f0 f0 ff 42434445 00000000 [root@guest ~]# lschp CHPID Vary Cfg. Type Cmg Shared PCHID ============================================ 0.00 1 - 32 - - - 0.42 1 3 1b - - - 0.43 1 3 1b - - - 0.44 1 3 1b - - - 0.45 1 3 1b - - - 3. On the host, configure off one path. [root@host ~]# chchp -c 0 42 4. On the guest, check the status: [root@guest ~]# lscss 0002 Device Subchan. DevType CU Type Use PIM PAM POM CHPIDs ---------------------------------------------------------------------- 0.0.3f3f 0.0.0002 3390/0c 3990/e9 f0 f0 ff 42434445 00000000 #Notice: No change! [root@localhost ~]# chccwdev -e 3f3f Setting device 0.0.3f3f online dasd-eckd 0.0.3f3f: A channel path to the device has become operational dasd-eckd 0.0.3f3f: New DASD 3390/0C (CU 3990/01) with 30051 cylinders, 15 heads, 224 sectors dasd-eckd 0.0.3f3f: DASD with 4 KB/block, 21636720 KB total size, 48 KB/track, compatible disk layout dasda:VOL1/ 0X3F3F: dasda1 Done [root@guest ~]# lscss 0002 Device Subchan. DevType CU Type Use PIM PAM POM CHPIDs ---------------------------------------------------------------------- 0.0.3f3f 0.0.0002 3390/0c 3990/e9 f0 70 ff 42434445 00000000 #Notice: PAM value of path 0.42 changed. 5. On the host, configure on one path. [root@host ~]# chchp -c 1 42 6. On the guest, check the status again: [root@guest ~]# lscss 0002 Device Subchan. DevType CU Type Use PIM PAM POM CHPIDs ---------------------------------------------------------------------- 0.0.3f3f 0.0.0002 3390/0c 3990/e9 f0 70 ff 42434445 00000000 #Notice: No change! [root@localhost ~]# chccwdev -d 3f3f Setting device 0.0.3f3f offline Done [root@guest ~]# lscss 0002 Device Subchan. DevType CU Type Use PIM PAM POM CHPIDs ---------------------------------------------------------------------- 0.0.3f3f 0.0.0002 3390/0c 3990/e9 f0 f0 ff 42434445 00000000 #Notice: PAM changed again. Dong Jia Shi (3): vfio: ccw: introduce schib region vfio: ccw: introduce channel path irq vfio: ccw: handle chp event drivers/s390/cio/vfio_ccw_drv.c | 51 +++++++++++++++++ drivers/s390/cio/vfio_ccw_fsm.c | 43 ++++++++++++++ drivers/s390/cio/vfio_ccw_ops.c | 108 ++++++++++++++++++++++++++---------- drivers/s390/cio/vfio_ccw_private.h | 8 +++ include/uapi/linux/vfio.h | 2 + include/uapi/linux/vfio_ccw.h | 6 ++ 6 files changed, 190 insertions(+), 28 deletions(-) -- 2.13.5
