linux-kernel - Re: [PATCH v3 1/3] s390x: KVM: accept STSI for CPU topology information

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Message-ID: <b5ee1953-b19d-50ec-b2e2-47a05babcee4@redhat.com>
Date:   Tue, 31 Aug 2021 15:59:04 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Pierre Morel <pmorel@...ux.ibm.com>, kvm@...r.kernel.org
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        borntraeger@...ibm.com, frankja@...ux.ibm.com, cohuck@...hat.com,
        thuth@...hat.com, imbrenda@...ux.ibm.com, hca@...ux.ibm.com,
        gor@...ux.ibm.com
Subject: Re: [PATCH v3 1/3] s390x: KVM: accept STSI for CPU topology
 information

On 03.08.21 10:26, Pierre Morel wrote:
> 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@...ux.ibm.com>
> ---
>   arch/s390/kvm/priv.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
> index 9928f785c677..8581b6881212 100644
> --- a/arch/s390/kvm/priv.c
> +++ b/arch/s390/kvm/priv.c
> @@ -856,7 +856,8 @@ 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) {
> +	if ((fc > 3 && fc != 15) ||
> +	    (fc == 15 && !test_kvm_facility(vcpu->kvm, 11))) {
>   		kvm_s390_set_psw_cc(vcpu, 3);
>   		return 0;
>   	}
> @@ -893,6 +894,10 @@ static int handle_stsi(struct kvm_vcpu *vcpu)
>   			goto out_no_data;
>   		handle_stsi_3_2_2(vcpu, (void *) mem);
>   		break;
> +	case 15:
> +		trace_kvm_s390_handle_stsi(vcpu, fc, sel1, sel2, operand2);
> +		insert_stsi_usr_data(vcpu, operand2, ar, fc, sel1, sel2);
> +		return -EREMOTE;
>   	}
>   	if (kvm_s390_pv_cpu_is_protected(vcpu)) {
>   		memcpy((void *)sida_origin(vcpu->arch.sie_block), (void *)mem,
> 

Sorry, I'm a bit rusty on s390x kvm facility handling.


For test_kvm_facility() to succeed, the facility has to be in both:

a) fac_mask: actually available on the HW and supported by KVM 
(kvm_s390_fac_base via FACILITIES_KVM, kvm_s390_fac_ext via 
FACILITIES_KVM_CPUMODEL)

b) fac_list: enabled for a VM

AFAIU, facility 11 is neither in FACILITIES_KVM nor 
FACILITIES_KVM_CPUMODEL, and I remember it's a hypervisor-managed bit.

So unless we unlock facility 11 in FACILITIES_KVM_CPUMODEL, will 
test_kvm_facility(vcpu->kvm, 11) ever successfully trigger here?


I'm pretty sure I am messing something up :)

-- 
Thanks,

David / dhildenb