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

[Janis Schoetterl-Glausch]

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@xxxxxxxxxxxxx>
> Reviewed-by: Nico Boehr <nrb@xxxxxxxxxxxxx>
> ---
>  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.

> +	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
> +	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

>  	}
>  	if (kvm_s390_pv_cpu_is_protected(vcpu)) {
>  		memcpy((void *)sida_origin(vcpu->arch.sie_block), (void *)mem,
> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
> index dada78b92691..94138f8f0c1c 100644
> --- a/arch/s390/kvm/vsie.c
> +++ b/arch/s390/kvm/vsie.c
> @@ -503,6 +503,14 @@ static int shadow_scb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>  	/* Host-protection-interruption introduced with ESOP */
>  	if (test_kvm_cpu_feat(vcpu->kvm, KVM_S390_VM_CPU_FEAT_ESOP))
>  		scb_s->ecb |= scb_o->ecb & ECB_HOSTPROTINT;
> +	/*
> +	 * 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
> +	 */
> +	if (test_kvm_facility(vcpu->kvm, 11))
> +		scb_s->ecb |= scb_o->ecb & ECB_PTF;
>  	/* transactional execution */
>  	if (test_kvm_facility(vcpu->kvm, 73) && wants_tx) {
>  		/* remap the prefix is tx is toggled on */