* Dong Jia Shi <bjsdj...@linux.vnet.ibm.com> [2017-09-26 15:48:56 +0800]:
[...] > > > > > > Tried to test with the following method: > > > 1. Start g1 (first level guest on kvm a host) with a virtio blk device > > > defined: > > > -drive > > > file=/dev/disk/by-path/ccw-0.0.3f3e,if=none,id=drive-virtio-disk1,format=raw > > > \ > > > -device > > > virtio-blk-ccw,devno=fe.0.2222,scsi=off,drive=drive-virtio-disk1,id=virtio-disk1 > > > \ > > > 2. Login g1, and bind the subchannel of ccw device 0.0.2222 with > > > vfio-ccw drvier. > > > 3. Create a mdev on the above subchannel. > > > 4. Passthrough the mdev to g2, and try to start g2. > > > > > > The 4th step failed with the following message and hang: > > > qemu-system-s390x: vfio-ccw: wirte I/O region: errno=4 > > > (BTW, 4 is EINTR.) > > > > > > I roughly guess this might be caused by: > > > On the kvm host, virtio callback injects the I/O interrupt in a > > > synchronzing manner. And this causes g1's I/O interrupt handler getting > > > the interrupt and then signaling the Qemu instance on g1 with the I/O > > > result, even before return of the pwrite(). > > > > > > But, using gdb on the kvm host, I do see several ssch successfully > > > executed. I will dig the root reason, and see if there is some way to > > > fix the issue. > > > > Hm... would that be the ccws used for setting up a virtio device, and > > the problems start once adapter interrupts become active? > After a debugging, when starting g2, I got the following ccw sequence: > 1. CCW_CMD_SENSE_ID 0xe4 [OK] > 2. CCW_CMD_NOOP 0x03 [OK] > 3. CCW_CMD_SET_VIRTIO_REV 0x83 [OK] > 4. CCW_CMD_VDEV_RESET 0x33 [FAILED] > > So this is still in the phase of setting up the device. > > > Does it work if you modify the nested guest to use the old > > per-subchannel indicators mechanism? > It turns out the root reason for the pwrite failure is caused by a bug > in the vfio-ccw driver: > drivers/s390/cio/vfio_ccw_cp.c: ccwchain_fetch_direct() > calls pfn_array_alloc_pin() with a zero @len parameter. > So it results in a -EINVAL return. > > The current code assumes that a valid direct ccw always has its count > value not equal to zero. However this is not true at least for the > CCW_CMD_VDEV_RESET (0x33) command: > (gdb) p/x ccw > $5 = {cmd_code = 0x33, flags = 0x4, count = 0x0, cda = 0x0} > > With a temp fix on this problem, more ccws (e.g. 0x11, 0x12, 0x31, 0x72 > ...) could be translated and executed well. But finnaly the qemu process > on g1 got a segmentation fault: > User process fault: interruption code 0238 ilc:3 in > libpthread-2.24.so[3ff84f80000+1b000] > Failing address: 000ce330b0b00000 TEID: 000ce330b0b00800 > Fault in primary space mode while using user ASCE. > AS:000000003b6cc1c7 R3:0000000000000024 > Segmentation fault > > dmesg on g1: > [ 18.160413] User process fault: interruption code 0238 ilc:3 in > libpthread-2.24.so[3ff84f80000+1b000] > [ 18.160462] Failing address: 000ce330b0b00000 TEID: 000ce330b0b00800 > [ 18.160463] Fault in primary space mode while using user ASCE. > [ 18.160470] AS:000000003b6cc1c7 R3:0000000000000024 > [ 18.160476] CPU: 1 PID: 2095 Comm: qemu-system-s39 Not tainted > 4.13.0-01250-g6baa298-dirty #58 > [ 18.160477] Hardware name: IBM 2964 NC9 704 (KVM/Linux) > [ 18.160479] task: 0000000038ac8000 task.stack: 0000000038e4c000 > [ 18.160480] User PSW : 0705200180000000 000003ff84f93b8a > [ 18.160483] R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:1 AS:0 CC:2 PM:0 > RI:0 EA:3 > [ 18.160486] User GPRS: 0000000000000001 000003ff00000003 0000000104be86b0 > 0000000104be86c6 > [ 18.160487] 0000000000000000 0000000100000001 00000001049efb22 > 000003ffc5dfe13f > [ 18.160489] 000003ff643fee60 0000000000000000 000003ffc5dfe258 > 000003ff643fe8c8 > [ 18.160490] 000003ff855a5000 00000001049cc320 000003ff643fe888 > 000003ff643fe7e8 > [ 18.160503] User Code: 000003ff84f93b7a: c0e5ffffe7cb brasl > %r14,3ff84f90b10 > 000003ff84f93b80: a7f4ffc4 brc > 15,3ff84f93b08 > #000003ff84f93b84: e5600000ff0c tbegin 0,65292 > >000003ff84f93b8a: b2220050 ipm >%r5 > 000003ff84f93b8e: 8850001c srl %r5,28 > 000003ff84f93b92: a774001c brc > 7,3ff84f93bca > 000003ff84f93b96: e30020000012 lt %r0,0(%r2) > 000003ff84f93b9c: a784ffb6 brc > 8,3ff84f93b08 > [ 18.160520] Last Breaking-Event-Address: > [ 18.160524] [<00000001046404e6>] 0x1046404e6 > > The above fault is not caused by vfio-ccw directly I think. So now I > need to install gdb stuff on g1, and continuing debugging. But ideas on > this are welcomed. ;) Using gdb with Qemu on g1, I got the following information: Thread 3 "qemu-system-s39" received signal SIGSEGV, Segmentation fault. [Switching to Thread 0x3ffdcdff910 (LWP 2095)] __lll_lock_elision (futex=0x1007686b0 <qemu_global_mutex>, adapt_count=0x1007686c6 <qemu_global_mutex+22>, private=0) at ../sysdeps/unix/sysv/linux/s390/elision-lock.c:66 66 ../sysdeps/unix/sysv/linux/s390/elision-lock.c: No such file or directory. (gdb) bt #0 __lll_lock_elision (futex=0x1007686b0 <qemu_global_mutex>, adapt_count=0x1007686c6 <qemu_global_mutex+22>, private=0) at ../sysdeps/unix/sysv/linux/s390/elision-lock.c:66 #1 0x000003fffd98a1f4 in __GI___pthread_mutex_lock (mutex=<optimized out>) at ../nptl/pthread_mutex_lock.c:92 #2 0x0000000100515326 in qemu_mutex_lock ( mutex=0x1007686b0 <qemu_global_mutex>) at util/qemu-thread-posix.c:65 #3 0x00000001000f2dec in qemu_mutex_lock_iothread () at /root/qemu/cpus.c:1581 #4 0x000000010022827e in kvm_arch_handle_exit (cs=0x100c30ce0, run=0x3fffce80000) at /root/qemu/target/s390x/kvm.c:2193 #5 0x0000000100131c40 in kvm_cpu_exec (cpu=0x100c30ce0) at /root/qemu/accel/kvm/kvm-all.c:2094 #6 0x00000001000f1d2a in qemu_kvm_cpu_thread_fn (arg=0x100c30ce0) at /root/qemu/cpus.c:1128 #7 0x000003fffd9879d4 in start_thread (arg=0x3ffdcdff910) at pthread_create.c:335 #8 0x000003fffd8736ae in thread_start () at ../sysdeps/unix/sysv/linux/s390/s390-64/clone.S:71 PC not saved Googled lock elision for a while, and I still have no idea on this problem. Any suggestions on this? -- Dong Jia Shi