On 6/28/22 12:58, Pierre Morel wrote: > > > On 6/28/22 10:59, Janis Schoetterl-Glausch wrote: >> On 6/20/22 14:54, Pierre Morel wrote: >>> We report a topology change to the guest for any CPU hotplug. >>> >>> The reporting to the guest is done using the Multiprocessor >>> Topology-Change-Report (MTCR) bit of the utility entry in the guest's >>> SCA which will be cleared during the interpretation of PTF. >>> >>> On every vCPU creation we set the MCTR bit to let the guest know the >>> next time he uses the PTF with command 2 instruction that the >>> topology changed and that he should use the STSI(15.1.x) instruction >>> to get the topology details. >>> >>> STSI(15.1.x) gives information on the CPU configuration topology. >>> Let's accept the interception of STSI with the function code 15 and >>> let the userland part of the hypervisor handle it when userland >>> support the CPU Topology facility. >>> >>> Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx> >>> --- >>> arch/s390/include/asm/kvm_host.h | 11 ++++++++--- >>> arch/s390/kvm/kvm-s390.c | 27 ++++++++++++++++++++++++++- >>> arch/s390/kvm/priv.c | 15 +++++++++++---- >>> arch/s390/kvm/vsie.c | 3 +++ >>> 4 files changed, 48 insertions(+), 8 deletions(-) >>> >> [...] >> >>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >>> index 8fcb56141689..95b96019ca8e 100644 >>> --- a/arch/s390/kvm/kvm-s390.c >>> +++ b/arch/s390/kvm/kvm-s390.c >>> @@ -1691,6 +1691,25 @@ static int kvm_s390_get_cpu_model(struct kvm *kvm, struct kvm_device_attr *attr) >>> return ret; >>> } >>> >>> +/** >>> + * kvm_s390_sca_set_mtcr >> >> I wonder if there is a better name, kvm_s390_report_topology_change maybe? >> >>> + * @kvm: guest KVM description >>> + * >>> + * Is only relevant if the topology facility is present, >>> + * the caller should check KVM facility 11 >>> + * >>> + * Updates the Multiprocessor Topology-Change-Report to signal >>> + * the guest with a topology change. >>> + */ >>> +static void kvm_s390_sca_set_mtcr(struct kvm *kvm) >>> +{ >> >> Do we need a sca_lock read_section here? If we don't why not? >> Did not see one up the stack, but I might have overlooked something. > > Yes we do. > As I said about your well justified comment in a previous mail, ipte_lock is not the right thing to use here and I will replace with an inter locked update. Not sure I'm understanding you right, you're saying we need both? i.e.: struct bsca_block *sca; read_lock(&vcpu->kvm->arch.sca_lock); sca = kvm->arch.sca; atomic_or(SCA_UTILITY_MTCR, &sca->utility); read_unlock(&vcpu->kvm->arch.sca_lock); Obviously you would need to change the definition of the utility field and could not use a bit field like Janosch suggested, unless you want to use a cmpxchg loop. It's a bit ugly that utility is a two byte value. Maybe there is a nicer way to set that bit, OR (OI, OIY) seem appropriate, but I don't know if they have a nice abstraction in Linux or if you'd need inline asm. > >> >>> + struct bsca_block *sca = kvm->arch.sca; /* SCA version doesn't matter */ >>> + >>> + ipte_lock(kvm); >>> + sca->utility |= SCA_UTILITY_MTCR; >>> + ipte_unlock(kvm); >>> +} >>> + >> >> [...] >> >