Messages in this thread |  | | Date | Tue, 28 Jun 2022 17:44:12 +0200 | Subject | Re: [PATCH v10 2/3] KVM: s390: guest support for topology function | From | Pierre Morel <> |
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On 6/28/22 17:01, Janis Schoetterl-Glausch wrote: > On 6/28/22 16:13, Pierre Morel wrote: >> >> >> On 6/28/22 14:18, Janis Schoetterl-Glausch wrote: >>> 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@linux.ibm.com> >>>>>> --- >>>>>> 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. >> >> I was think to something like this because it is what is used most of the time when a bit is to be change concurrently with firmware. > > Ah, ok you want to keep the bitfield. > > [...] >> >> static void kvm_s390_sca_set_mtcr(struct kvm *kvm, int val) > > If you use a bool val you can simply do new.mtcr = val; below. >> { >> struct bsca_block *sca = kvm->arch.sca; >> union sca_utility new, old; >> >> read_lock(&kvm->arch.sca_lock); > > Don't forget to move the sca = kvm->arch.sca; under the lock here. >> do { >> old = READ_ONCE(sca->utility); >> new = old; >> new.mtcr = val ? 1 : 0; >> } while (cmpxchg(&sca->utility.val, old.val, new.val) != old.val); >> read_lock(&kvm->arch.sca_lock); >> }
right, thanks, and to unlock at the end :)
>> >>>> >>>>> >>>>>> + struct bsca_block *sca = kvm->arch.sca; /* SCA version doesn't matter */ >>>>>> + >>>>>> + ipte_lock(kvm); >>>>>> + sca->utility |= SCA_UTILITY_MTCR; >>>>>> + ipte_unlock(kvm); >>>>>> +} >>>>>> + >>>>> >>>>> [...] >>>>> >>>> >>> >> >
-- Pierre Morel IBM Lab Boeblingen
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