Messages in this thread |  | | Date | Tue, 28 Jun 2022 16:13:00 +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 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.
+union sca_utility { + __u16 val; + struct { + __u16 mtcr : 1; + __u16 reserved : 15; + }; +}; + struct bsca_block { union ipte_control ipte_control; __u64 reserved[5]; __u64 mcn; - __u64 reserved2; + union sca_utility utility; + __u8 reserved2[6]; struct bsca_entry cpu[KVM_S390_BSCA_CPU_SLOTS]; }
....
static void kvm_s390_sca_set_mtcr(struct kvm *kvm, int val) { struct bsca_block *sca = kvm->arch.sca; union sca_utility new, old;
read_lock(&kvm->arch.sca_lock); 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); }
>> >>> >>>> + 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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