linux-kernel - Re: [PATCH v10 2/3] KVM: s390: guest support for topology function

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Message-ID: <165605380436.8840.11959073846437899088@localhost.localdomain>
Date:   Fri, 24 Jun 2022 08:56:44 +0200
From:   Nico Boehr <nrb@...ux.ibm.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,
        david@...hat.com, thuth@...hat.com, imbrenda@...ux.ibm.com,
        hca@...ux.ibm.com, gor@...ux.ibm.com, pmorel@...ux.ibm.com,
        wintera@...ux.ibm.com, seiden@...ux.ibm.com
Subject: Re: [PATCH v10 2/3] KVM: s390: guest support for topology function

Quoting Pierre Morel (2022-06-20 14:54:36)
[...]
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index 766028d54a3e..bb54196d4ed6 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
[...]
> @@ -3403,6 +3426,8 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
>         rc = kvm_s390_vcpu_setup(vcpu);
>         if (rc)
>                 goto out_ucontrol_uninit;
> +
> +       kvm_s390_sca_set_mtcr(vcpu->kvm);

We set the MTCR in the vcpu create. Does it also make sense to set it in kvm_arch_vcpu_destroy?

[...]
> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
> index 12c464c7cddf..77a692238585 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)
[...]
> +       case 15:
> +               trace_kvm_s390_handle_stsi(vcpu, fc, sel1, sel2, operand2);
> +               insert_stsi_usr_data(vcpu, operand2, ar, fc, sel1, sel2);
> +               return -EREMOTE;

Maybe the API documentation should clearly note that once you turn on KVM_CAP_S390_CPU_TOPOLOGY, you will get exits to userspace for STSI 15.x.y, regardless of whether KVM_CAP_S390_USER_STSI is on or off.

Other than that, looks good, hence:

Reviewed-by: Nico Boehr <nrb@...ux.ibm.com>