Xen on FreeBSD 11: Cannot boot from QCOW2 properly (waiting for XENBUS, xenbusb_nop_confighook_cb)

["Roger Pau Monné"]

On Tue, Jan 24, 2017 at 05:45:25PM +0300, Alexander Nusov wrote:
> Yes, it was FreeBSD 11.0-STABLE Dom0 with xen-kernel/xen-tools built from the ports tree (head)
> 
> 
> 
> It seems there is an issue with xen pci devices, since booting from QCOW2 images actually works (even on FreeBSD 11.0-RELEASE branch) except communication with /xen/vbd devices from the guest.

Yes, I'm seeing exactly the same. The QEMU process is killed with a
segmentation fault. Akshay, here is the full debug output:

Program terminated with signal 11, Segmentation fault.
[...]
#0  blk_handle_requests (blkdev=0x807463c00) at hw/block/xen_disk.c:862
862	    rp = blkdev->rings.common.sring->req_prod;
[New Thread 8087f9000 (LWP 100947/<unknown>)]
[New Thread 807418800 (LWP 100945/<unknown>)]
[New Thread 807418300 (LWP 100944/<unknown>)]
[New Thread 807417e00 (LWP 100943/<unknown>)]
[New Thread 807417900 (LWP 100942/<unknown>)]
[New Thread 807417400 (LWP 100941/<unknown>)]
[New Thread 807416a00 (LWP 100940/<unknown>)]
[New Thread 807416500 (LWP 100939/<unknown>)]
[New Thread 807416000 (LWP 100091/<unknown>)]
(gdb) bt
#0  blk_handle_requests (blkdev=0x807463c00) at hw/block/xen_disk.c:862
#1  0x00000000005f9dcd in blk_bh (opaque=0x807463c00) at hw/block/xen_disk.c:918
#2  0x000000000080ba69 in aio_bh_call (bh=0x80780d810) at async.c:87
#3  0x000000000080bb10 in aio_bh_poll (ctx=0x8074a0680) at async.c:115
#4  0x000000000081c099 in aio_dispatch (ctx=0x8074a0680) at aio-posix.c:303
#5  0x000000000080c2cd in aio_ctx_dispatch (source=0x8074a0680, callback=0, user_data=0x0)
    at async.c:254
#6  0x0000000802e3903b in g_main_context_dispatch () from /usr/local/lib/libglib-2.0.so.0
#7  0x000000000081a34c in glib_pollfds_poll () at main-loop.c:259
#8  0x0000000000819dc5 in os_host_main_loop_wait (timeout=0) at main-loop.c:306
#9  0x0000000000819c29 in main_loop_wait (nonblocking=0) at main-loop.c:556
#10 0x0000000000588ed7 in main_loop () at vl.c:1966
#11 0x0000000000583b59 in main (argc=38, argv=0x7fffffffe750, envp=0x7fffffffe888) at vl.c:4684
Current language:  auto; currently minimal

It seems like the device is not properly mapping the grants, and QEMU gets a
SEGFAULT when trying to access the ring page.

Roger.