On Fri, Sep 29, 2023 at 8:39 PM Daniel P. Berrangé <berra...@redhat.com> wrote: > > On Tue, Sep 26, 2023 at 03:31:09PM -0300, Daniel Henrique Barboza wrote: > > At this moment we do not expose extension properties for vendor CPUs > > because that would allow users to change them via command line. The > > drawback is that if we were to add an API that shows all CPU properties, > > e.g. qmp-query-cpu-model-expansion, we won't be able to show extensions > > state of vendor CPUs. > > > > We have the required machinery to create extension properties for vendor > > CPUs while not allowing users to enable extensions. Disabling existing > > extensions is allowed since it can be useful for debugging. > > > > Change the set() callback cpu_set_multi_ext_cfg() to allow enabling > > extensions only for generic CPUs. In cpu_add_multi_ext_prop() let's not > > set the default values for the properties if we're not dealing with > > generic CPUs, otherwise the values set in cpu_init() of vendor CPUs will > > be overwritten. And finally, in tcg_cpu_instance_init(), add cpu user > > properties for all CPUs. > > > > For the veyron-v1 CPU, we're now able to disable existing extensions > > like smstateen: > > > > $ ./build/qemu-system-riscv64 --nographic -M virt \ > > -cpu veyron-v1,smstateen=false > > > > But setting extensions that the CPU didn't set during cpu_init(), like > > V, is not allowed: > > > > $ ./build/qemu-system-riscv64 --nographic -M virt \ > > -cpu veyron-v1,v=true > > qemu-system-riscv64: can't apply global veyron-v1-riscv-cpu.v=true: > > 'veyron-v1' CPU does not allow enabling extensions > > Why should we block the user if they want to enable an extra > feature, over and above what is built-in to the CPU model ?
It ends up being tricky to maintain. On top of that we can report a specific vendor CPU to guests, but then we don't correctly model it (as extensions might be disabled). Alistair > Is there some technical reason that prevents this from working ? > > With regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| > >
