Thanks, but I don't understand why nobody mentions actually WHY it is being locked. I eventually found the answer by listening to Alex Williamson <https://www.youtube.com/watch?v=WFkdTFTOTpA&t=1099s>'s talk on the subject, where he mentions that IOMMU chips lack "page faulting" machanism. He also suggests that it may be possible that in the future it will be added to x86 PCs, so I think that it is important that we talk about it rather than just take this memory pinning situation for granted. Thanks for mentioning memory hotplugging - I've looked into virtio-mem project, which seems to address this, but as you mentioned (and thank you for stating it clearly as it took me a long time to figure it out) it requires manual interventions from the admin. Best wishes, Daniel On 20/09/2023 16:59, Daniel P. Berrangé wrote:

...

Hi

I'm trying to Passthrough a GPU to a VM and have it still share its free memory with the host (just like it would with virtio-balloon). Is this something virtio-mem is capable of? I've tried to run it, but it immediately took over 9GB of memory:

virt-install --name test --cpu cell0.cpus=0,cell0.memory=4194304,cell1.cpus=1,cell1.memory=4194304 --memory maxMemory=65536,maxMemory.slots=8 --memdev model=virtio-mem,target.node=0,target.block=2048,target.size=1000 --disk size=400 --network network=ai --location=/tmp/debian-12.1.0-amd64-netinst.iso --os-variant=debian11 --graphics none --extra-args "console=ttyS0 When using PCI device assignment, the VFIO driver requires that libvit

On Fri, Sep 15, 2023 at 02:41:50AM +0100, Daniel Krajnik wrote: pin guest memory into RAM

https://gitlab.com/libvirt/libvirt/-/blob/19484ccac5cb1586f9d10d3e6eb9b93ee8...

so that's why you'll see the immediate memory usage. I dont' think there's any way to workaround this limitation automatically. Closest you can get is to actually hot-unplug the RAM your guest isn't using, but that needs manual work to re-hot-plug it if the guest later needs more RAM, so that's not very friendly.

With regards, Daniel