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

[Pierre Morel <pmorel@linux.ibm.com>]

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