Re: [PATCH v11 2/3] KVM: s390: guest support for topology function

Pierre Morel
2022-07-04T10:57:52Z

On 7/4/22 11:08, Janis Schoetterl-Glausch wrote:
> On 7/1/22 18:25, 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
> s/he/it (twice)
>> 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.And the user STSI capability.
> Also: supportS.
>>
>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>> Reviewed-by: Nico Boehr <nrb@linux.ibm.com>
>> ---
>> arch/s390/include/asm/kvm_host.h | 18 +++++++++++++---
>> arch/s390/kvm/kvm-s390.c | 36 ++++++++++++++++++++++++++++++++
>> arch/s390/kvm/priv.c | 16 ++++++++++----
>> arch/s390/kvm/vsie.c | 8 +++++++
>> 4 files changed, 71 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
>> index 766028d54a3e..ae6bd3d607de 100644
>> --- a/arch/s390/include/asm/kvm_host.h
>> +++ b/arch/s390/include/asm/kvm_host.h
>> @@ -93,19 +93,30 @@ union ipte_control {
>> };
>> };
>>
> [...]
>
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index 8fcb56141689..ee59b03f2e45 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -1691,6 +1691,31 @@ static int kvm_s390_get_cpu_model(struct kvm *kvm, struct kvm_device_attr *attr)
>> return ret;
>> }
>>
>> +/**
>> + * kvm_s390_update_topology_change_report - update CPU topology change report
>> + * @kvm: guest KVM description
>> + * @val: set or clear the MTCR bit
>> + *
>> + * Updates the Multiprocessor Topology-Change-Report bit to signal
>> + * the guest with a topology change.
>> + * This is only relevant if the topology facility is present.
>> + *
>> + * The SCA version, bsca or esca, doesn't matter as offset is the same.
>> + */
>> +static void kvm_s390_update_topology_change_report(struct kvm *kvm, bool val)
>> +{
>> + struct bsca_block *sca = kvm->arch.sca;
>> + union sca_utility new, old;
>> +
>> + read_lock(&kvm->arch.sca_lock);
>
> You forgot to put the assignment of sca under the lock.

Should I really?
What we want to protect here is the content of the sca.
The sca itself does not change during the life of the KVM AFAIK.

>
>> + do {
>> + old = READ_ONCE(sca->utility);
>> + new = old;
>> + new.mtcr = val;
>> + } while (cmpxchg(&sca->utility.val, old.val, new.val) != old.val);
>> + read_unlock(&kvm->arch.sca_lock);
>> +}
>> +
>> static int kvm_s390_vm_set_attr(struct kvm *kvm, struct kvm_device_attr *attr)
>> {
>> int ret;
>> @@ -2877,6 +2902,7 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
>> kvm_clear_async_pf_completion_queue(vcpu);
>> if (!kvm_is_ucontrol(vcpu->kvm))
>> sca_del_vcpu(vcpu);
>> + kvm_s390_update_topology_change_report(vcpu->kvm, 1);
>>
>> if (kvm_is_ucontrol(vcpu->kvm))
>> gmap_remove(vcpu->arch.gmap);
>> @@ -3272,6 +3298,14 @@ static int kvm_s390_vcpu_setup(struct kvm_vcpu *vcpu)
>> vcpu->arch.sie_block->ecb |= ECB_HOSTPROTINT;
>> if (test_kvm_facility(vcpu->kvm, 9))
>> vcpu->arch.sie_block->ecb |= ECB_SRSI;
>> + /*
>> + * CPU Topology
>> + * This facility only uses the utility field of the SCA and none
>> + * of the cpu entries that are problematic with the other
>> + * interpretation facilities so we can pass it through.
>> + */
>
> This is the comment for vsie.c

right

>> + if (test_kvm_facility(vcpu->kvm, 11))
>> + vcpu->arch.sie_block->ecb |= ECB_PTF;
>> if (test_kvm_facility(vcpu->kvm, 73))
>> vcpu->arch.sie_block->ecb |= ECB_TE;
>> if (!kvm_is_ucontrol(vcpu->kvm))
>> @@ -3403,6 +3437,8 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
>> rc = kvm_s390_vcpu_setup(vcpu);
>> if (rc)
>> goto out_ucontrol_uninit;
>> +
>> + kvm_s390_update_topology_change_report(vcpu->kvm, 1);
>> return 0;
>>
>> out_ucontrol_uninit:
>> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
>> index 12c464c7cddf..046afee1be94 100644
>> --- a/arch/s390/kvm/priv.c
>> +++ b/arch/s390/kvm/priv.c
>> @@ -873,10 +873,13 @@ static int handle_stsi(struct kvm_vcpu *vcpu)
>> if (vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE)
>> return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP);
>>
>> - if (fc > 3) {
>> - kvm_s390_set_psw_cc(vcpu, 3);
>> - return 0;
>> - }
>> + /* Bailout forbidden function codes */
>> + if (fc > 3 && (fc != 15 || kvm_s390_pv_cpu_is_protected(vcpu)))
>> + goto out_no_data;
>> +
>> + /* fc 15 is provided with PTF/CPU topology support */
>> + if (fc == 15 && !test_kvm_facility(vcpu->kvm, 11))
>> + goto out_no_data;
>>
>> if (vcpu->run->s.regs.gprs[0] & 0x0fffff00
>> || vcpu->run->s.regs.gprs[1] & 0xffff0000)
>> @@ -910,6 +913,11 @@ static int handle_stsi(struct kvm_vcpu *vcpu)
>> goto out_no_data;
>> handle_stsi_3_2_2(vcpu, (void *) mem);
>> break;
>> + case 15: /* fc 15 is fully handled in userspace */
>> + if (vcpu->kvm->arch.user_stsi)
>> + insert_stsi_usr_data(vcpu, operand2, ar, fc, sel1, sel2);
>> + trace_kvm_s390_handle_stsi(vcpu, fc, sel1, sel2, operand2);
>> + return -EREMOTE;
>
> This doesn't look right to me, you still return -EREMOTE if user_stsi is false.
> The way I read the PoP here is that it is ok to set condition code 3 for the else case

Yes it is what I wanted to do.
I do not understand what I did here is stupid.

--
Pierre Morel
IBM Lab Boeblingen