Here's a qtest reproducer: cat << EOF | ./i386-softmmu/qemu-system-i386 \ -device nec-usb-xhci -trace usb\* \ -device usb-audio -device usb-storage,drive=mydrive \ -drive id=mydrive,file=null-co://,size=2M,format=raw,if=none \ -nodefaults -nographic -qtest stdio outl 0xcf8 0x80001016 outl 0xcfc 0x3c319f0d outl 0xcf8 0x80001004 outl 0xcfc 0xc77695e writel 0x9f0d000000000040 0xffffd855 write 0x1d 0x1 0x27 write 0x2d 0x1 0x2e write 0x17232 0x1 0x03 write 0x17254 0x1 0x05 write 0x17276 0x1 0x72 write 0x17278 0x1 0x02 write 0x3d 0x1 0x27 write 0x40 0x1 0x2e write 0x41 0x1 0x72 write 0x42 0x1 0x01 write 0x4d 0x1 0x2e write 0x4f 0x1 0x01 writeq 0x9f0d000000002000 0x5c05140100000000 writeq 0x9f0d000000002000 0x5c05140100000000 write 0x2008d 0x1 0x13 writeq 0x9f0d000000002000 0x100ef0100000009 write 0x200ad 0x1 0x27 write 0x200bd 0x1 0x5c write 0x200cd 0x1 0x2e write 0x200dd 0x1 0x2f write 0x200e8 0x1 0x08 write 0x200ec 0x1 0xfe write 0x200ed 0x1 0x08 write 0x200fd 0x1 0x05 write 0x2010d 0x1 0x2e write 0x2011d 0x1 0x2f write 0x2012d 0x1 0x08 write 0x20137 0x1 0x5e write 0x2013a 0x1 0x2f write 0x2013d 0x1 0x05 write 0x2014d 0x1 0x13 writeq 0x9f0d000000002000 0x100ef0100000009 EOF ... [S +0.017146] OK [R +0.017149] writeq 0x9f0d000000002000 0x5c05140100000000 30899@1597183147.299108:usb_xhci_doorbell_write off 0x0000, val 0x00000000 30899@1597183147.299112:usb_xhci_fetch_trb addr 0x0000000000000000, TRB_RESERVED, p 0x0000000000000000, s 0x00000000, c 0x00000000 30899@1597183147.299115:usb_xhci_doorbell_write off 0x0004, val 0x5c051401 OK [S +0.017162] OK [R +0.017166] writeq 0x9f0d000000002000 0x5c05140100000000 30899@1597183147.299124:usb_xhci_doorbell_write off 0x0000, val 0x00000000 30899@1597183147.299126:usb_xhci_fetch_trb addr 0x0000000000000010, CR_ENABLE_SLOT, p 0x0000000000000000, s 0x00000000, c 0x00002700 30899@1597183147.299129:usb_xhci_slot_enable slotid 1 30899@1597183147.299132:usb_xhci_fetch_trb addr 0x0000000000000020, CR_ADDRESS_DEVICE, p 0x0000000000000000, s 0x00000000, c 0x00002e00 30899@1597183147.299134:usb_xhci_fetch_trb addr 0x0000000000000030, CR_ENABLE_SLOT, p 0x0000000000000000, s 0x00000000, c 0x00002700 30899@1597183147.299137:usb_xhci_slot_enable slotid 2 30899@1597183147.299139:usb_xhci_fetch_trb addr 0x0000000000000040, CR_ADDRESS_DEVICE, p 0x000000000001722e, s 0x00000000, c 0x01002e00 30899@1597183147.299144:usb_xhci_slot_address slotid 1, port 1 30899@1597183147.299148:usb_xhci_ep_enable slotid 1, epid 1 30899@1597183147.299151:usb_xhci_fetch_trb addr 0x0000000000000050, TRB_RESERVED, p 0x0000000000000000, s 0x00000000, c 0x00000000 30899@1597183147.299154:usb_xhci_doorbell_write off 0x0004, val 0x5c051401 30899@1597183147.299157:usb_xhci_ep_kick slotid 1, epid 1, streamid 23557 30899@1597183147.299161:usb_xhci_fetch_trb addr 0x0000000000020070, TRB_RESERVED, p 0x0000000000000000, s 0x00000000, c 0x00000000 OK [S +0.017210] OK [R +0.017214] write 0x2008d 0x1 0x13 OK [S +0.017219] OK [R +0.017223] writeq 0x9f0d000000002000 0x100ef0100000009 30899@1597183147.299181:usb_xhci_doorbell_write off 0x0000, val 0x00000009 30899@1597183147.299183:usb_xhci_doorbell_write off 0x0004, val 0x0100ef01 30899@1597183147.299185:usb_xhci_ep_kick slotid 1, epid 1, streamid 256 30899@1597183147.299189:usb_xhci_fetch_trb addr 0x0000000000020080, TR_STATUS, p 0x0000000000000000, s 0x00000000, c 0x00001300 30899@1597183147.299191:usb_xhci_xfer_start 0x5622548f9760: slotid 1, epid 1, streamid 0 TRB_SETUP 1300 1300 1300 0 30899@1597183147.299196:usb_xhci_fetch_trb addr 0x0000000000020090, TRB_RESERVED, p 0x0000000000000000, s 0x00000000, c 0x00000000 OK [S +0.017244] OK [R +0.017248] write 0x200ad 0x1 0x27 OK [S +0.017338] OK [R +0.017342] writeq 0x9f0d000000002000 0x100ef0100000009 30899@1597183147.299300:usb_xhci_doorbell_write off 0x0000, val 0x00000009 30899@1597183147.299302:usb_xhci_doorbell_write off 0x0004, val 0x0100ef01 30899@1597183147.299304:usb_xhci_ep_kick slotid 1, epid 1, streamid 256 30899@1597183147.299308:usb_xhci_fetch_trb addr 0x00000000000200a0, CR_ENABLE_SLOT, p 0x0000000000000000, s 0x00000000, c 0x00002700 30899@1597183147.299310:usb_xhci_xfer_start 0x5622548f9890: slotid 1, epid 1, streamid 0 TRB_SETUP 2700 2700 2700 0 30899@1597183147.299315:usb_xhci_fetch_trb addr 0x00000000000200b0, CR_NOOP, p 0x0000000000000000, s 0x00000000, c 0x00005c00 30899@1597183147.299318:usb_xhci_xfer_start 0x5622548f99a0: slotid 1, epid 1, streamid 0 TRB_SETUP 5c00 5c00 5c00 0 30899@1597183147.299322:usb_xhci_fetch_trb addr 0x00000000000200c0, CR_ADDRESS_DEVICE, p 0x0000000000000000, s 0x00000000, c 0x00002e00 30899@1597183147.299325:usb_xhci_xfer_start 0x5622548f9ab0: slotid 1, epid 1, streamid 0 TRB_SETUP 2e00 2e00 2e00 0 30899@1597183147.299329:usb_xhci_fetch_trb addr 0x00000000000200d0, CR_ADDRESS_DEVICE, p 0x0000000000000000, s 0x00000000, c 0x00002f00 30899@1597183147.299331:usb_xhci_xfer_start 0x5622548f9c10: slotid 1, epid 1, streamid 0 TRB_SETUP 2f00 2f00 2f00 0 30899@1597183147.299337:usb_xhci_fetch_trb addr 0x00000000000200e0, TR_SETUP, p 0x0000000000000000, s 0x00000008, c 0x000008fe 30899@1597183147.299340:usb_xhci_fetch_trb addr 0x00000000000200f0, TR_NORMAL, p 0x0000000000000000, s 0x00000000, c 0x00000500 30899@1597183147.299342:usb_xhci_fetch_trb addr 0x0000000000020100, CR_ADDRESS_DEVICE, p 0x0000000000000000, s 0x00000000, c 0x00002e00 30899@1597183147.299345:usb_xhci_fetch_trb addr 0x0000000000020110, CR_ADDRESS_DEVICE, p 0x0000000000000000, s 0x00000000, c 0x00002f00 30899@1597183147.299348:usb_xhci_fetch_trb addr 0x0000000000020120, TR_SETUP, p 0x0000000000000000, s 0x00000000, c 0x00000800 30899@1597183147.299351:usb_xhci_fetch_trb addr 0x0000000000020130, TR_NORMAL, p 0x5e00000000000000, s 0x002f0000, c 0x00000500 30899@1597183147.299353:usb_xhci_fetch_trb addr 0x0000000000020140, TR_STATUS, p 0x0000000000000000, s 0x00000000, c 0x00001300 30899@1597183147.299356:usb_xhci_xfer_start 0x5622548f9d70: slotid 1, epid 1, streamid 0 TRB_SETUP 8fe 1300 8fe 8 30899@1597183147.299361:usb_packet_state_change bus 0, port 1, ep 0, packet 0x5622548f9d78, state undef -> setup 30899@1597183147.299466:usb_packet_state_change bus 0, port 1, ep 0, packet 0x5622548f9d78, state setup -> complete qemu-system-i386: /home/alxndr/Development/qemu/general-fuzz/exec.c:3623: void address_space_unmap(AddressSpace *, void *, hwaddr, _Bool, hwaddr): Assertion `mr != NULL' failed. #8 0x7f8f9e7e6091 in __assert_fail /build/glibc-GwnBeO/glibc-2.30/assert/assert.c:101:3 #9 0x55f7507b374a in address_space_unmap exec.c:3623:9 #10 0x55f750baeab8 in dma_memory_unmap include/sysemu/dma.h:145:5 #11 0x55f750baea1b in usb_packet_unmap hw/usb/libhw.c:65:9 #12 0x55f750bcbb73 in xhci_xfer_unmap hw/usb/hcd-xhci.c:1487:5 #13 0x55f750bcba3d in xhci_try_complete_packet hw/usb/hcd-xhci.c:1642:9 #14 0x55f750bcc888 in xhci_fire_ctl_transfer hw/usb/hcd-xhci.c:1728:5 #15 0x55f750bcb306 in xhci_kick_epctx hw/usb/hcd-xhci.c:1991:13 #16 0x55f750bd04e9 in xhci_kick_ep hw/usb/hcd-xhci.c:1861:5 #17 0x55f750bd253c in xhci_doorbell_write hw/usb/hcd-xhci.c:3162:13 #18 0x55f75091def1 in memory_region_write_accessor softmmu/memory.c:483:5 #19 0x55f75091ddf3 in access_with_adjusted_size softmmu/memory.c:544:18 #20 0x55f75091dac5 in memory_region_dispatch_write softmmu/memory.c #21 0x55f7507b51e2 in flatview_write_continue exec.c:3176:23 #22 0x55f7507b2a30 in flatview_write exec.c:3216:14 #23 0x55f7507b2968 in address_space_write exec.c:3308:18 #24 0x55f750929e3b in qtest_process_command softmmu/qtest.c