* Jaggi, Manish (manish.ja...@cavium.com) wrote: > Just to add what happens in ARM64 case, qemu running on Machine A sends cpu > state information to Machine B. > This state contains MIDR value, and so Processor ID value is compared in KVM > and not in qemu (correcting myself). > > IIRC, Peter/Eric please point if there is something incorrect in the below > flow... > > (Machine B) > target/arm/machine.c: cpu_post_load() > - updates cpu->cpreg_values[i] : which includes MIDR (processor > ID register) > > - calls write_list_to_kvmstate(cpu, KVM_PUT_FULL_STATE) > > target/arm/kvm.c: write_list_to_kvmstate > - calls => kvm_vcpu_ioctl(cs, KVM_SET_ONE_REG, > &r); > > => and it eventually lands up IIRC in > Linux code in > > => > arch/arm64/kvm/sys_regs.c : set_invariant_sys_reg(u64 id, void __user *uaddr) > /* This is what > we mean by invariant: you can't change it. */ > if (r->val != > val) > return > -EINVAL; > Note: MIDR_EL1 > is invariant register. > result: Migration fails on Machine B. > > A few points: > - qemu on arm64 is invoked with -machine virt and -cpu as host. So we don't > explicitly define which cpu.
Note that even on x86 we don't guarantee as much about '-cpu host', what we expect to work for migration is that if you pick a '-cpu amodel' and both hosts support the feature flags required by 'amodel' then it should work. > - In case Machine A and Machine B have almost same Core and the delta may-not > have any effect on qemu operation, migration should work by just looking into > whitelist. > whitelist can be given as a parameter for qemu on machine B. > > qemu-system-aarch64 -whitelist <ids separated by commas> > > (This is my proposal) > > - So in cpu_post_load (Machine B) qemu can lookup whitelist and replace the > MIDR with the one at Machine B. > Sounds good? > > - Juan raised a point about clock speed, I am not sure it will have any > effect on arm since qemu is run with -cpu host param. > I could be wrong here, Peter/Eric can you please correct me... Clock speed is only really a problem for things like timestamp counters; some cores let you scale them; for those that don't then yes it's a bit odd. Dave > -Thanks > Manish > > > > > Dave > >> - is providing a -mirate-compat-whitelist <file> option for arm only looks > >> good? > >> this option can be added in A1/A2 qemu command, so it would be upstream / > >> downstream agnostic. > > > >>> > >>> I am sorry to not be able to tell you that this is an easy problem. > >>> > >>> Later, Juan. > >> > > -- > > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK > -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
