[Qemu-devel] virtio_stw_phys_cached crash

[Fam Zheng]

On master (13b7b188501) and v3.0.0, booting the OpenBSD install63.iso with a
virtio-net (slirp backend) device gives this assertion failure:

(gdb) bt
#0  0x00007f6f25703feb in raise () at /lib64/libc.so.6
#1  0x00007f6f256ee5c1 in abort () at /lib64/libc.so.6
#2  0x00007f6f256ee491 in _nl_load_domain.cold.0 () at /lib64/libc.so.6
#3  0x00007f6f256fc752 in  () at /lib64/libc.so.6
#4  0x000055d966f5b5d6 in address_space_stw_le_cached (cache=0x7f6f040fd700, 
addr=516, val=1, attrs=..., result=0x0)
    at /stor/work/qemu/include/exec/memory_ldst_cached.inc.h:85
#5  0x000055d966f5b804 in stw_le_phys_cached (cache=0x7f6f040fd700, addr=516, 
val=1) at /stor/work/qemu/include/exec/memory_ldst_phys.inc.h:121
#6  0x000055d966f5c3e7 in virtio_stw_phys_cached (vdev=0x55d969aeeff0, 
cache=0x7f6f040fd700, pa=516, value=1) at 
/stor/work/qemu/include/hw/virtio/virtio-access.h:195
#7  0x000055d966f5cef8 in vring_set_avail_event (vq=0x7f6f181df110, val=1) at 
/stor/work/qemu/hw/virtio/virtio.c:324
#8  0x000055d966f5e1c8 in virtqueue_pop (vq=0x7f6f181df110, sz=48) at 
/stor/work/qemu/hw/virtio/virtio.c:883
#9  0x000055d966f2d69b in virtio_net_handle_ctrl (vdev=0x55d969aeeff0, 
vq=0x7f6f181df110) at /stor/work/qemu/hw/net/virtio-net.c:986
#10 0x000055d966f5ffb9 in virtio_queue_notify_vq (vq=0x7f6f181df110) at 
/stor/work/qemu/hw/virtio/virtio.c:1534
#11 0x000055d966f6224d in virtio_queue_host_notifier_read (n=0x7f6f181df178) at 
/stor/work/qemu/hw/virtio/virtio.c:2451
#12 0x000055d9673ef460 in aio_dispatch_handlers (ctx=0x55d96891af90) at 
/stor/work/qemu/util/aio-posix.c:406
#13 0x000055d9673ef5f3 in aio_dispatch (ctx=0x55d96891af90) at 
/stor/work/qemu/util/aio-posix.c:437
#14 0x000055d9673eae25 in aio_ctx_dispatch (source=0x55d96891af90, 
callback=0x0, user_data=0x0) at /stor/work/qemu/util/async.c:261
#15 0x00007f6f28b578ad in g_main_context_dispatch () at /lib64/libglib-2.0.so.0
#16 0x000055d9673ee040 in glib_pollfds_poll () at 
/stor/work/qemu/util/main-loop.c:215
#17 0x000055d9673ee0ae in os_host_main_loop_wait (timeout=0) at 
/stor/work/qemu/util/main-loop.c:238
#18 0x000055d9673ee167 in main_loop_wait (nonblocking=0) at 
/stor/work/qemu/util/main-loop.c:497
#19 0x000055d96702efd0 in main_loop () at /stor/work/qemu/vl.c:1866
#20 0x000055d9670368bd in main (argc=22, argv=0x7ffdef327638, 
envp=0x7ffdef3276f0) at /stor/work/qemu/vl.c:4644

No surprise, bisection points to

commit 48564041a73adbbff52834f9edbe3806fceefab7
Author: Paolo Bonzini <address@hidden>
Date:   Sun Mar 18 18:26:36 2018 +0100

    exec: reintroduce MemoryRegion caching

Fam