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

Janis Schoetterl-Glausch
2022-06-24T15:09:53Z

On 6/20/22 14:54, 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
> 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.
>
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
> arch/s390/include/asm/kvm_host.h | 11 ++++++++---
> arch/s390/kvm/kvm-s390.c | 27 ++++++++++++++++++++++++++-
> arch/s390/kvm/priv.c | 15 +++++++++++----
> arch/s390/kvm/vsie.c | 3 +++
> 4 files changed, 48 insertions(+), 8 deletions(-)
>
[...]

> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 8fcb56141689..95b96019ca8e 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -1691,6 +1691,25 @@ static int kvm_s390_get_cpu_model(struct kvm *kvm, struct kvm_device_attr *attr)
> return ret;
> }
>
> +/**
> + * kvm_s390_sca_set_mtcr
> + * @kvm: guest KVM description
> + *
> + * Is only relevant if the topology facility is present,
> + * the caller should check KVM facility 11
> + *
> + * Updates the Multiprocessor Topology-Change-Report to signal
> + * the guest with a topology change.
> + */
> +static void kvm_s390_sca_set_mtcr(struct kvm *kvm)
> +{
> + struct bsca_block *sca = kvm->arch.sca; /* SCA version doesn't matter */
> +
> + ipte_lock(kvm);

Why do we need to take the ipte lock here and in patch 3?

> + sca->utility |= SCA_UTILITY_MTCR;
> + ipte_unlock(kvm);
> +} …