Re: [PATCH v4 3/4] KVM: s390: Add UV feature negotiation

[Michael Mueller <mimu@linux.ibm.com>]

On 15.08.23 17:14, Steffen Eiden wrote:
> Add a uv_feature list for pv-guests to the KVM cpu-model.
> The feature bits 'AP-interpretation for secure guests' and
> 'AP-interrupt for secure guests' are available.
> 
> Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>
> Reviewed-by: Janosch Frank <frankja@linux.ibm.com>

Reviewed-by: Michael Mueller <mimu@linux.ibm.com>

but a minor comment, see below.

> ---
>   arch/s390/include/asm/kvm_host.h |  2 +
>   arch/s390/include/uapi/asm/kvm.h | 16 +++++++
>   arch/s390/kvm/kvm-s390.c         | 73 ++++++++++++++++++++++++++++++++
>   3 files changed, 91 insertions(+)
> 
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index 91bfecb91321..427f9528a7b6 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -817,6 +817,8 @@ struct kvm_s390_cpu_model {
>   	__u64 *fac_list;
>   	u64 cpuid;
>   	unsigned short ibc;
> +	/* subset of available UV-features for pv-guests enabled by user space */
> +	struct kvm_s390_vm_cpu_uv_feat uv_feat_guest;
>   };
> 
>   typedef int (*crypto_hook)(struct kvm_vcpu *vcpu);
> diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h
> index a73cf01a1606..abe926d43cbe 100644
> --- a/arch/s390/include/uapi/asm/kvm.h
> +++ b/arch/s390/include/uapi/asm/kvm.h
> @@ -159,6 +159,22 @@ struct kvm_s390_vm_cpu_subfunc {
>   	__u8 reserved[1728];
>   };
> 
> +#define KVM_S390_VM_CPU_PROCESSOR_UV_FEAT_GUEST	6
> +#define KVM_S390_VM_CPU_MACHINE_UV_FEAT_GUEST	7
> +
> +#define KVM_S390_VM_CPU_UV_FEAT_NR_BITS	64
> +struct kvm_s390_vm_cpu_uv_feat {
> +	union {
> +		struct {
> +			__u64 : 4;
> +			__u64 ap : 1;		/* bit 4 */
> +			__u64 ap_intr : 1;	/* bit 5 */
> +			__u64 : 58;
> +		};
> +		__u64 feat;
> +	};
> +};
> +
>   /* kvm attributes for crypto */
>   #define KVM_S390_VM_CRYPTO_ENABLE_AES_KW	0
>   #define KVM_S390_VM_CRYPTO_ENABLE_DEA_KW	1
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 813cc3d59c90..b3f17e014cab 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -1531,6 +1531,39 @@ static int kvm_s390_set_processor_subfunc(struct kvm *kvm,
>   	return 0;
>   }
> 
> +#define KVM_S390_VM_CPU_UV_FEAT_GUEST_MASK	\
> +(						\
> +	((struct kvm_s390_vm_cpu_uv_feat){	\
> +		.ap = 1,			\
> +		.ap_intr = 1,			\
> +	})					\
> +	.feat					\
> +)
> +
> +static int kvm_s390_set_uv_feat(struct kvm *kvm, struct kvm_device_attr *attr)
> +{
> +	struct kvm_s390_vm_cpu_uv_feat __user *ptr = (void __user *)attr->addr;
> +	unsigned long data, filter;
> +
> +	filter = uv_info.uv_feature_indications & KVM_S390_VM_CPU_UV_FEAT_GUEST_MASK;

if get_user() fails the uv feature bits in "filter" are
calculated in vain

> +	if (get_user(data, &ptr->feat))
> +		return -EFAULT;

could be done here, but that's really minor to me

> +	if (!bitmap_subset(&data, &filter, KVM_S390_VM_CPU_UV_FEAT_NR_BITS))
> +		return -EINVAL;
> +
> +	mutex_lock(&kvm->lock);
> +	if (kvm->created_vcpus) {
> +		mutex_unlock(&kvm->lock);
> +		return -EBUSY;
> +	}
> +	kvm->arch.model.uv_feat_guest.feat = data;
> +	mutex_unlock(&kvm->lock);
> +
> +	VM_EVENT(kvm, 3, "SET: guest UV-feat: 0x%16.16lx", data);
> +
> +	return 0;
> +}
> +
>   static int kvm_s390_set_cpu_model(struct kvm *kvm, struct kvm_device_attr *attr)
>   {
>   	int ret = -ENXIO;
> @@ -1545,6 +1578,9 @@ static int kvm_s390_set_cpu_model(struct kvm *kvm, struct kvm_device_attr *attr)
>   	case KVM_S390_VM_CPU_PROCESSOR_SUBFUNC:
>   		ret = kvm_s390_set_processor_subfunc(kvm, attr);
>   		break;
> +	case KVM_S390_VM_CPU_PROCESSOR_UV_FEAT_GUEST:
> +		ret = kvm_s390_set_uv_feat(kvm, attr);
> +		break;
>   	}
>   	return ret;
>   }
> @@ -1777,6 +1813,33 @@ static int kvm_s390_get_machine_subfunc(struct kvm *kvm,
>   	return 0;
>   }
> 
> +static int kvm_s390_get_processor_uv_feat(struct kvm *kvm, struct kvm_device_attr *attr)
> +{
> +	struct kvm_s390_vm_cpu_uv_feat __user *dst = (void __user *)attr->addr;
> +	unsigned long feat = kvm->arch.model.uv_feat_guest.feat;
> +
> +	if (put_user(feat, &dst->feat))
> +		return -EFAULT;
> +	VM_EVENT(kvm, 3, "GET: guest UV-feat: 0x%16.16lx", feat);
> +
> +	return 0;
> +}
> +
> +static int kvm_s390_get_machine_uv_feat(struct kvm *kvm, struct kvm_device_attr *attr)
> +{
> +	struct kvm_s390_vm_cpu_uv_feat __user *dst = (void __user *)attr->addr;
> +	unsigned long feat;
> +
> +	BUILD_BUG_ON(sizeof(*dst) != sizeof(uv_info.uv_feature_indications));
> +
> +	feat = uv_info.uv_feature_indications & KVM_S390_VM_CPU_UV_FEAT_GUEST_MASK;
> +	if (put_user(feat, &dst->feat))
> +		return -EFAULT;
> +	VM_EVENT(kvm, 3, "GET: guest UV-feat: 0x%16.16lx", feat);
> +
> +	return 0;
> +}
> +
>   static int kvm_s390_get_cpu_model(struct kvm *kvm, struct kvm_device_attr *attr)
>   {
>   	int ret = -ENXIO;
> @@ -1800,6 +1863,12 @@ static int kvm_s390_get_cpu_model(struct kvm *kvm, struct kvm_device_attr *attr)
>   	case KVM_S390_VM_CPU_MACHINE_SUBFUNC:
>   		ret = kvm_s390_get_machine_subfunc(kvm, attr);
>   		break;
> +	case KVM_S390_VM_CPU_PROCESSOR_UV_FEAT_GUEST:
> +		ret = kvm_s390_get_processor_uv_feat(kvm, attr);
> +		break;
> +	case KVM_S390_VM_CPU_MACHINE_UV_FEAT_GUEST:
> +		ret = kvm_s390_get_machine_uv_feat(kvm, attr);
> +		break;
>   	}
>   	return ret;
>   }
> @@ -1952,6 +2021,8 @@ static int kvm_s390_vm_has_attr(struct kvm *kvm, struct kvm_device_attr *attr)
>   		case KVM_S390_VM_CPU_MACHINE_FEAT:
>   		case KVM_S390_VM_CPU_MACHINE_SUBFUNC:
>   		case KVM_S390_VM_CPU_PROCESSOR_SUBFUNC:
> +		case KVM_S390_VM_CPU_MACHINE_UV_FEAT_GUEST:
> +		case KVM_S390_VM_CPU_PROCESSOR_UV_FEAT_GUEST:
>   			ret = 0;
>   			break;
>   		default:
> @@ -3296,6 +3367,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>   	kvm->arch.model.cpuid = kvm_s390_get_initial_cpuid();
>   	kvm->arch.model.ibc = sclp.ibc & 0x0fff;
> 
> +	kvm->arch.model.uv_feat_guest.feat = 0;
> +
>   	kvm_s390_crypto_init(kvm);
> 
>   	if (IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM)) {