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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>
25 lines
739 B
XML
25 lines
739 B
XML
<domain type='kvm'>
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<name>guest</name>
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<memory unit='KiB'>1048576</memory>
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<vcpu placement='static'>1</vcpu>
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<os>
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<type arch='x86_64' machine='pc'>hvm</type>
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</os>
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<devices>
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<emulator>/usr/bin/qemu-system-x86_64</emulator>
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<disk type='nvme' device='disk'>
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<driver name='qemu' type='raw'/>
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<source type='pci' managed='yes' namespace='1'>
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<address domain='0x0003' bus='0x02' slot='0x00' function='0x0'/>
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</source>
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<target dev='vda' bus='virtio'/>
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</disk>
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<hostdev mode='subsystem' type='pci' managed='yes'>
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<driver name='vfio'/>
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<source>
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<address domain='0x0001' bus='0x01' slot='0x00' function='0x0'/>
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</source>
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</hostdev>
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</devices>
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</domain>
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