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>

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

@@ -0,0 +1,24 @@
+<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>

tests/qemumemlocktest.c

@@ -97,6 +97,7 @@ mymain(void)
     DO_TEST("pc-hardlimit", 2147483648);
     DO_TEST("pc-locked", VIR_DOMAIN_MEMORY_PARAM_UNLIMITED);
     DO_TEST("pc-hostdev", 2147483648);
+    DO_TEST("pc-hostdev-nvme", 3221225472);
 
     DO_TEST("pc-hardlimit+locked", 2147483648);
     DO_TEST("pc-hardlimit+hostdev", 2147483648);