When passing-through via vfio-pci using QEMU 7.1.0 and OVMF, it appears that qemu preallocates all guest system memory.
qemu-system-x86_64 \ -no-user-config \ -nodefaults \ -nographic \ -rtc base=utc \ -boot strict=on \ -machine pc,accel=kvm,dump-guest-core=off \ -cpu host,migratable=off \ -smp 8 \ -m size=8G \ -overcommit mem-lock=off \ -device vfio-pci,host=03:00.0 \ ... PID USER PR NI VIRT RES %CPU %MEM TIME+ S COMMAND 4151 root 20 0 13560.8m *8310.8m* 100.0 52.6 0:25.06 S qemu-system-x86_64 If I remove just the vfio-pci device argument, it appears that qemu no longer preallocates all guest system memory. PID USER PR NI VIRT RES %CPU %MEM TIME+ S COMMAND 5049 root 20 0 13414.0m *762.4m* 0.0 4.8 0:27.06 S qemu-system-x86_64 I am curious if anyone has any context on or experience with this functionality. Does anyone know if preallocation is a requirement for VFIO with QEMU or if preallocation can be disabled? I am speculating that QEMU is actually preallocating as opposed to the guest touching every page of system memory. Thanks.
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