linux-kernel - Re: [PATCH v9 2/3] s390x: KVM: guest support for topology function

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Date:   Thu, 12 May 2022 11:24:38 +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, wintera@...ux.ibm.com, seiden@...ux.ibm.com,
        nrb@...ux.ibm.com
Subject: Re: [PATCH v9 2/3] s390x: KVM: guest support for topology function

On 06.05.22 11:24, Pierre Morel wrote:
> We let the userland hypervisor know if the machine support the CPU
> topology facility using a new KVM capability: KVM_CAP_S390_CPU_TOPOLOGY.
> 
> The PTF instruction will report a topology change if there is any change
> with a previous STSI_15_1_2 SYSIB.
> Changes inside a STSI_15_1_2 SYSIB occur if CPU bits are set or clear
> inside the CPU Topology List Entry CPU mask field, which happens with
> changes in CPU polarization, dedication, CPU types and adding or
> removing CPUs in a socket.
> 
> The reporting to the guest is done using the Multiprocessor
> Topology-Change-Report (MTCR) bit of the utility entry of the guest's
> SCA which will be cleared during the interpretation of PTF.
> 
> To check if the topology has been modified we use a new field of the
> arch vCPU to save the previous real CPU ID at the end of a schedule
> and verify on next schedule that the CPU used is in the same socket.
> We do not report polarization, CPU Type or dedication change.
> 
> 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>

[...]


> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
> index 0e8603acc105..d9e16b09c8bf 100644
> --- a/arch/s390/kvm/priv.c
> +++ b/arch/s390/kvm/priv.c
> @@ -874,10 +874,12 @@ 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;
> -	}
> +	if (fc > 3 && fc != 15)
> +		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;


Maybe shorter as

if (fc == 15 && !test_kvm_facility(vcpu->kvm, 11))
	goto out_no_data;
else if (fc > 3)
	goto out_no_data;


Apart from that, LGTM.

-- 
Thanks,

David / dhildenb