libvirt/tests/qemumemlockdata/qemumemlock-pc-hostdev-nvme.xml

<domain type='kvm'>
  <name>guest</name>
  <memory unit='KiB'>1048576</memory>
  <vcpu placement='static'>1</vcpu>
  <os>
    <type arch='x86_64' machine='pc'>hvm</type>
  </os>
  <devices>
    <emulator>/usr/bin/qemu-system-x86_64</emulator>
    <disk type='nvme' device='disk'>
      <driver name='qemu' type='raw'/>
      <source type='pci' managed='yes' namespace='1'>
        <address domain='0x0003' bus='0x02' slot='0x00' function='0x0'/>
      </source>
      <target dev='vda' bus='virtio'/>
    </disk>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <driver name='vfio'/>
      <source>
        <address domain='0x0001' bus='0x01' slot='0x00' function='0x0'/>
      </source>
    </hostdev>
  </devices>
</domain>
qemu_domain: Increase memlock limit for NVMe disks When starting QEMU, or when hotplugging a PCI device QEMU might lock some memory. How much? Well, that's an undecidable problem. But despite that, we try to guess. And it more or less works, until there's a counter example. This time, it's a guest with both <hostdev/> and an NVMe <disk/>. I've started a simple guest with 4GiB of memory: # virsh dominfo fedora Max memory: 4194304 KiB Used memory: 4194304 KiB And here are the amounts of memory that QEMU tried to lock, obtained via: grep VmLck /proc/$(pgrep qemu-kvm)/status 1) with just one <hostdev/> VmLck: 4194308 kB 2) with just one NVMe <disk/> VmLck: 4328544 kB 3) with one <hostdev/> and one NVMe <disk/> VmLck: 8522852 kB Now, what's surprising is case 2) where the locked memory exceeds the VM memory. It almost resembles VDPA. Therefore, treat is as such. Unfortunately, I don't have a box with two or more spare NVMe-s so I can't tell for sure. But setting limit too tight means QEMU refuses to start. Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2014030 Signed-off-by: Michal Privoznik <mprivozn@redhat.com> Reviewed-by: Martin Kletzander <mkletzan@redhat.com> 2023-04-12 15:15:08 +00:00			`<domain type='kvm'>`
			`<name>guest</name>`
			`<memory unit='KiB'>1048576</memory>`
			`<vcpu placement='static'>1</vcpu>`
			`<os>`
			`<type arch='x86_64' machine='pc'>hvm</type>`
			`</os>`
			`<devices>`
			`<emulator>/usr/bin/qemu-system-x86_64</emulator>`
			`<disk type='nvme' device='disk'>`
			`<driver name='qemu' type='raw'/>`
			`<source type='pci' managed='yes' namespace='1'>`
			`<address domain='0x0003' bus='0x02' slot='0x00' function='0x0'/>`
			`</source>`
			`<target dev='vda' bus='virtio'/>`
			`</disk>`
			`<hostdev mode='subsystem' type='pci' managed='yes'>`
			`<driver name='vfio'/>`
			`<source>`
			`<address domain='0x0001' bus='0x01' slot='0x00' function='0x0'/>`
			`</source>`
			`</hostdev>`
			`</devices>`
			`</domain>`