[Qemu-devel] [Bug 1813940] Re: kvm_mem_ioeventfd_add: error adding ioeventfd: No space left on device

[Paolo Bonzini]

Hmm that's not surprising because coalesced ranges were completely
broken before that commit.  I'll take a look.

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Title:
  kvm_mem_ioeventfd_add: error adding ioeventfd: No space left on device

Status in QEMU:
  New

Bug description:
  Latest QEMU master fails to run with too many MMIO devices specified.

  After patch 3ac7d43a6fb [1] QEMU just prints an error message and exits.
  > kvm_mem_ioeventfd_add: error adding ioeventfd: No space left on device

  This is reproducible e.g. with the following setup:

  qemu-3.1.50-dirty \
      -machine pc-i440fx-2.7,accel=kvm \
      -cpu host -m 4096 \
      -smp 2,sockets=2,cores=1,threads=1 \
      -drive file=freebsd_vm_1.qcow2,format=qcow2,if=none,id=bootdr \
      -device ide-hd,drive=bootdr,bootindex=0 \
      -device virtio-scsi-pci,id=vc0 \
      -device virtio-scsi-pci,id=vc1 \
      -device virtio-scsi-pci,id=vc2 \
      -device virtio-scsi-pci,id=vc3 \

  Running with just 3 Virtio-SCSI controllers seems to work fine, adding
  more than that causes the error above. Note that this is not Virtio-
  SCSI specific. I've also reproduced this without any Virtio devices
  whatsoever.

  strace shows the following ioctl chain over and over:

  145787 ioctl(11, KVM_UNREGISTER_COALESCED_MMIO, 0x7f60a4985410) = 0
  145787 ioctl(11, KVM_UNREGISTER_COALESCED_MMIO, 0x7f60a4985410) = 0
  145787 ioctl(11, KVM_REGISTER_COALESCED_MMIO, 0x7f60a49853b0) = 0
  145787 ioctl(11, KVM_REGISTER_COALESCED_MMIO, 0x7f60a49853b0) = -1 ENOSPC (No 
space left on device)
  145787 ioctl(11, KVM_REGISTER_COALESCED_MMIO, 0x7f60a49853b0) = -1 ENOSPC (No 
space left on device)
  145787 ioctl(11, KVM_REGISTER_COALESCED_MMIO, 0x7f60a49853b0) = -1 ENOSPC (No 
space left on device)
  145787 ioctl(11, KVM_REGISTER_COALESCED_MMIO, 0x7f60a49853b0) = -1 ENOSPC (No 
space left on device)
  145787 ioctl(11, KVM_REGISTER_COALESCED_MMIO, 0x7f60a49853b0) = -1 ENOSPC (No 
space left on device)
  145787 ioctl(11, KVM_REGISTER_COALESCED_MMIO, 0x7f60a49853b0) = -1 ENOSPC (No 
space left on device)
  145787 ioctl(11, KVM_REGISTER_COALESCED_MMIO, 0x7f60a49853b0) = -1 ENOSPC (No 
space left on device)
  145787 ioctl(11, KVM_REGISTER_COALESCED_MMIO, 0x7f60a49853b0) = -1 ENOSPC (No 
space left on device)

  Which suggests there's some kind of MMIO region leak.

  [1]
  commit 3ac7d43a6fbb5d4a3d01fc9a055c218030af3727
  Author:     Paolo Bonzini <address@hidden>
  AuthorDate: Wed Nov 28 17:28:45 2018 +0100
  Commit:     Paolo Bonzini <address@hidden>
  CommitDate: Fri Jan 11 13:57:24 2019 +0100

      memory: update coalesced_range on transaction_commit

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