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It also depends on whether the > VMM has requested sve for a specific Guest or not(Qemu has option to > turn sve on/off, similarly pmu as well). Based on that KVM > populates the Guest specific ID registers. And Guest /proc/cpuinfo > reflects that. > > And for some features if KVM is not handling the feature properly or > not making any sense to be exposed to Guest, those features are > masked in ID registers. > > Recently ARM64 ID registers has been made writable from userspace to > allow VMM to turn on/off features, so that VMs can be migrated > between hosts that differ in feature support. > > https://lore.kernel.org/all/ZR2YfAixZgbCFnb8@linux.dev/T/#m7c2493fd2d43c13a3336d19f2dc06a89803c6fdb I see, so there is a significant difference - in KVM the kernel controls what ID values the VM observes and in vSMMU the VMM controls it. Jason