linux-kernel - Re: [PATCH v9 3/3] s390x: KVM: resetting the Topology-Change-Report

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Message-ID: <76fd0c11-5b9b-0032-183b-54db650f13b1@redhat.com>
Date:   Thu, 12 May 2022 11:31:18 +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 3/3] s390x: KVM: resetting the Topology-Change-Report

On 06.05.22 11:24, Pierre Morel wrote:
> During a subsystem reset the Topology-Change-Report is cleared.
> Let's give userland the possibility to clear the MTCR in the case
> of a subsystem reset.
> 
> To migrate the MTCR, let's give userland the possibility to
> query the MTCR state.
> 
> Signed-off-by: Pierre Morel <pmorel@...ux.ibm.com>
> ---
>  arch/s390/include/uapi/asm/kvm.h |  5 ++
>  arch/s390/kvm/kvm-s390.c         | 79 ++++++++++++++++++++++++++++++++
>  2 files changed, 84 insertions(+)
> 
> diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h
> index 7a6b14874d65..abdcf4069343 100644
> --- a/arch/s390/include/uapi/asm/kvm.h
> +++ b/arch/s390/include/uapi/asm/kvm.h
> @@ -74,6 +74,7 @@ struct kvm_s390_io_adapter_req {
>  #define KVM_S390_VM_CRYPTO		2
>  #define KVM_S390_VM_CPU_MODEL		3
>  #define KVM_S390_VM_MIGRATION		4
> +#define KVM_S390_VM_CPU_TOPOLOGY	5
>  
>  /* kvm attributes for mem_ctrl */
>  #define KVM_S390_VM_MEM_ENABLE_CMMA	0
> @@ -171,6 +172,10 @@ struct kvm_s390_vm_cpu_subfunc {
>  #define KVM_S390_VM_MIGRATION_START	1
>  #define KVM_S390_VM_MIGRATION_STATUS	2
>  
> +/* kvm attributes for cpu topology */
> +#define KVM_S390_VM_CPU_TOPO_MTR_CLEAR	0
> +#define KVM_S390_VM_CPU_TOPO_MTR_SET	1
> +
>  /* for KVM_GET_REGS and KVM_SET_REGS */
>  struct kvm_regs {
>  	/* general purpose regs for s390 */
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index c8bdce31464f..80a1244f0ead 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -1731,6 +1731,76 @@ static void kvm_s390_sca_set_mtcr(struct kvm *kvm)
>  	ipte_unlock(kvm);
>  }
>  
> +/**
> + * kvm_s390_sca_clear_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_clear_mtcr(struct kvm *kvm)
> +{
> +	struct bsca_block *sca = kvm->arch.sca; /* SCA version doesn't matter */
> +
> +	ipte_lock(kvm);
> +	sca->utility  &= ~SCA_UTILITY_MTCR;


One space too much.

sca->utility &= ~SCA_UTILITY_MTCR;

> +	ipte_unlock(kvm);
> +}
> +
> +static int kvm_s390_set_topology(struct kvm *kvm, struct kvm_device_attr *attr)
> +{
> +	if (!test_kvm_facility(kvm, 11))
> +		return -ENXIO;
> +
> +	switch (attr->attr) {
> +	case KVM_S390_VM_CPU_TOPO_MTR_SET:
> +		kvm_s390_sca_set_mtcr(kvm);
> +		break;
> +	case KVM_S390_VM_CPU_TOPO_MTR_CLEAR:
> +		kvm_s390_sca_clear_mtcr(kvm);
> +		break;
> +	}
> +	return 0;
> +}
> +
> +/**
> + * kvm_s390_sca_get_mtcr
> + * @kvm: guest KVM description
> + *
> + * Is only relevant if the topology facility is present,
> + * the caller should check KVM facility 11
> + *
> + * reports to QEMU the Multiprocessor Topology-Change-Report.
> + */
> +static int kvm_s390_sca_get_mtcr(struct kvm *kvm)
> +{
> +	struct bsca_block *sca = kvm->arch.sca; /* SCA version doesn't matter */
> +	int val;
> +
> +	ipte_lock(kvm);
> +	val = !!(sca->utility & SCA_UTILITY_MTCR);
> +	ipte_unlock(kvm);
> +
> +	return val;
> +}
> +
> +static int kvm_s390_get_topology(struct kvm *kvm, struct kvm_device_attr *attr)
> +{
> +	int mtcr;

I think we prefer something like u16 when copying to user space.

> +
> +	if (!test_kvm_facility(kvm, 11))
> +		return -ENXIO;
> +
> +	mtcr = kvm_s390_sca_get_mtcr(kvm);
> +	if (copy_to_user((void __user *)attr->addr, &mtcr, sizeof(mtcr)))
> +		return -EFAULT;
> +
> +	return 0;
> +}

You should probably add documentation, and document that only the last
bit (0x1) has a meaning.

Apart from that LGTM.

-- 
Thanks,

David / dhildenb