Re: [PATCH v7 20/22] KVM: s390: add KVM_S390_ZPCI_OP to manage guest zPCI devices

Thomas Huth
2022-05-16T09:52:16Z

On 13/05/2022 21.15, Matthew Rosato wrote:
> The KVM_S390_ZPCI_OP ioctl provides a mechanism for managing
> hardware-assisted virtualization features for s390X zPCI passthrough.

s/s390X/s390x/

> Add the first 2 operations, which can be used to enable/disable
> the specified device for Adapter Event Notification interpretation.
>
> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
> ---
> Documentation/virt/kvm/api.rst | 45 +++++++++++++++++++
> arch/s390/kvm/kvm-s390.c | 23 ++++++++++
> arch/s390/kvm/pci.c | 81 ++++++++++++++++++++++++++++++++++
> arch/s390/kvm/pci.h | 2 +
> include/uapi/linux/kvm.h | 31 +++++++++++++
> 5 files changed, 182 insertions(+)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 4a900cdbc62e..a7cd5ebce031 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -5645,6 +5645,51 @@ enabled with ``arch_prctl()``, but this may change in the future.
> The offsets of the state save areas in struct kvm_xsave follow the contents
> of CPUID leaf 0xD on the host.
>
> +4.135 KVM_S390_ZPCI_OP
> +--------------------
> +
> +:Capability: KVM_CAP_S390_ZPCI_OP
> +:Architectures: s390
> +:Type: vcpu ioctl

vcpu? ... you're wiring it up in kvm_arch_vm_ioctl() later, so I assume
it's rather a VM ioctl?

> +:Parameters: struct kvm_s390_zpci_op (in)
> +:Returns: 0 on success, <0 on error
> +
> +Used to manage hardware-assisted virtualization features for zPCI devices.
> +
> +Parameters are specified via the following structure::
> +
> + struct kvm_s390_zpci_op {
> + /* in */

If all is "in", why is there a copy_to_user() in the code later?

> + __u32 fh; /* target device */
> + __u8 op; /* operation to perform */
> + __u8 pad[3];
> + union {
> + /* for KVM_S390_ZPCIOP_REG_AEN */
> + struct {
> + __u64 ibv; /* Guest addr of interrupt bit vector */
> + __u64 sb; /* Guest addr of summary bit */

If this is really a vcpu ioctl, what kind of addresses are you talking about
here? virtual addresses? real addresses? absolute addresses?

> + __u32 flags;
> + __u32 noi; /* Number of interrupts */
> + __u8 isc; /* Guest interrupt subclass */
> + __u8 sbo; /* Offset of guest summary bit vector */
> + __u16 pad;
> + } reg_aen;
> + __u64 reserved[8];
> + } u;
> + };
> +
> +The type of operation is specified in the "op" field.
> +KVM_S390_ZPCIOP_REG_AEN is used to register the VM for adapter event
> +notification interpretation, which will allow firmware delivery of adapter
> +events directly to the vm, with KVM providing a backup delivery mechanism;
> +KVM_S390_ZPCIOP_DEREG_AEN is used to subsequently disable interpretation of
> +adapter event notifications.
> +
> +The target zPCI function must also be specified via the "fh" field. For the
> +KVM_S390_ZPCIOP_REG_AEN operation, additional information to establish firmware
> +delivery must be provided via the "reg_aen" struct.
> +
> +The "reserved" field is meant for future extensions.

Maybe also mention the "pad" fields? And add should these also be
initialized to 0 by the calling userspace program?

> 5. The kvm_run structure
> ========================
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index b95b25490018..1af7cea9d579 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -618,6 +618,12 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> case KVM_CAP_S390_PROTECTED:
> r = is_prot_virt_host();
> break;
> + case KVM_CAP_S390_ZPCI_OP:
> + if (kvm_s390_pci_interp_allowed())
> + r = 1;
> + else
> + r = 0;

Could be shortened to:

r = kvm_s390_pci_interp_allowed();

> + break;
> default:
> r = 0;
> }
> @@ -2633,6 +2639,23 @@ long kvm_arch_vm_ioctl(struct file *filp,
> r = -EFAULT;
> break;
> }
> + case KVM_S390_ZPCI_OP: {
> + struct kvm_s390_zpci_op args;
> +
> + r = -EINVAL;
> + if (!IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM))
> + break;
> + if (copy_from_user(&args, argp, sizeof(args))) {
> + r = -EFAULT;
> + break;
> + }
> + r = kvm_s390_pci_zpci_op(kvm, &args);
> + if (r)
> + break;
> + if (copy_to_user(argp, &args, sizeof(args)))
> + r = -EFAULT;

So this copy_to_user() indicates that information is returned to userspace
... but below, the ioctl is declared with _IOW only ... this does not match.
Should it be declared with _IOWR or should the copy_to_user() be dropped?

> + break;
> + }
> default:
> r = -ENOTTY;
> }
> diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
> index 1393a1604494..6e6254016be4 100644
> --- a/arch/s390/kvm/pci.c
> +++ b/arch/s390/kvm/pci.c
> @@ -585,6 +585,87 @@ void kvm_s390_pci_clear_list(struct kvm *kvm)
> spin_unlock(&kvm->arch.kzdev_list_lock);
> }
>
> +static struct zpci_dev *get_zdev_from_kvm_by_fh(struct kvm *kvm, u32 fh)
> +{
> + struct zpci_dev *zdev = NULL;
> + struct kvm_zdev *kzdev;
> +
> + spin_lock(&kvm->arch.kzdev_list_lock);
> + list_for_each_entry(kzdev, &kvm->arch.kzdev_list, entry) {
> + if (kzdev->zdev->fh == fh) {
> + zdev = kzdev->zdev;
> + break;
> + }
> + }
> + spin_unlock(&kvm->arch.kzdev_list_lock);
> +
> + return zdev;
> +}
> +
> +static int kvm_s390_pci_zpci_reg_aen(struct zpci_dev *zdev,
> + struct kvm_s390_zpci_op *args)
> +{
> + struct zpci_fib fib = {};
> +
> + fib.fmt0.aibv = args->u.reg_aen.ibv;
> + fib.fmt0.isc = args->u.reg_aen.isc;
> + fib.fmt0.noi = args->u.reg_aen.noi;
> + if (args->u.reg_aen.sb != 0) {
> + fib.fmt0.aisb = args->u.reg_aen.sb;
> + fib.fmt0.aisbo = args->u.reg_aen.sbo;
> + fib.fmt0.sum = 1;
> + } else {
> + fib.fmt0.aisb = 0;
> + fib.fmt0.aisbo = 0;
> + fib.fmt0.sum = 0;
> + }
> +
> + if (args->u.reg_aen.flags & KVM_S390_ZPCIOP_REGAEN_HOST)
> + return kvm_s390_pci_aif_enable(zdev, &fib, true);
> + else
> + return kvm_s390_pci_aif_enable(zdev, &fib, false);

Alternatively (just a matter of taste):

bool hostflag;
...
hostflag = (args->u.reg_aen.flags & KVM_S390_ZPCIOP_REGAEN_HOST);
return kvm_s390_pci_aif_enable(zdev, &fib, hostflag);

> +}
> +
> +int kvm_s390_pci_zpci_op(struct kvm *kvm, struct kvm_s390_zpci_op *args)
> +{
> + struct kvm_zdev *kzdev;
> + struct zpci_dev *zdev;
> + int r;
> +
> + zdev = get_zdev_from_kvm_by_fh(kvm, args->fh);
> + if (!zdev)
> + return -ENODEV;
> +
> + mutex_lock(&zdev->kzdev_lock);
> + mutex_lock(&kvm->lock);
> +
> + kzdev = zdev->kzdev;
> + if (!kzdev) {
> + r = -ENODEV;
> + goto out;
> + }
> + if (kzdev->kvm != kvm) {
> + r = -EPERM;
> + goto out;
> + }
> +
> + switch (args->op) {
> + case KVM_S390_ZPCIOP_REG_AEN:

Please also check here that args->u.reg_aen.flags does not have any bits set
that we don't support here (otherwise, this could cause some trouble when
introducing additional flags later).

> + r = kvm_s390_pci_zpci_reg_aen(zdev, args);
> + break;
> + case KVM_S390_ZPCIOP_DEREG_AEN:
> + r = kvm_s390_pci_aif_disable(zdev, false);
> + break;
> + default:
> + r = -EINVAL;
> + }
> +
> +out:
> + mutex_unlock(&kvm->lock);
> + mutex_unlock(&zdev->kzdev_lock);
> + return r;
> +}
> +
> int kvm_s390_pci_init(void)
> {
> aift = kzalloc(sizeof(struct zpci_aift), GFP_KERNEL);
> diff --git a/arch/s390/kvm/pci.h b/arch/s390/kvm/pci.h
> index fb2b91b76e0c..0351382e990f 100644
> --- a/arch/s390/kvm/pci.h
> +++ b/arch/s390/kvm/pci.h
> @@ -59,6 +59,8 @@ void kvm_s390_pci_aen_exit(void);
> void kvm_s390_pci_init_list(struct kvm *kvm);
> void kvm_s390_pci_clear_list(struct kvm *kvm);
>
> +int kvm_s390_pci_zpci_op(struct kvm *kvm, struct kvm_s390_zpci_op *args);
> +
> int kvm_s390_pci_init(void);
> void kvm_s390_pci_exit(void);
>
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 6a184d260c7f..1d3d41523d10 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1152,6 +1152,7 @@ struct kvm_ppc_resize_hpt {
> #define KVM_CAP_DISABLE_QUIRKS2 213
> /* #define KVM_CAP_VM_TSC_CONTROL 214 */
> #define KVM_CAP_SYSTEM_EVENT_DATA 215
> +#define KVM_CAP_S390_ZPCI_OP 216
>
> #ifdef KVM_CAP_IRQ_ROUTING
>
> @@ -2068,4 +2069,34 @@ struct kvm_stats_desc {
> /* Available with KVM_CAP_XSAVE2 */
> #define KVM_GET_XSAVE2 _IOR(KVMIO, 0xcf, struct kvm_xsave)
>
> +/* Available with KVM_CAP_S390_ZPCI_OP */
> +#define KVM_S390_ZPCI_OP _IOW(KVMIO, 0xd0, struct kvm_s390_zpci_op)

Please double-check whether this should be _IOWR instead (see above).

> +struct kvm_s390_zpci_op {
> + /* in */
> + __u32 fh; /* target device */
> + __u8 op; /* operation to perform */
> + __u8 pad[3];
> + union {
> + /* for KVM_S390_ZPCIOP_REG_AEN */
> + struct {
> + __u64 ibv; /* Guest addr of interrupt bit vector */
> + __u64 sb; /* Guest addr of summary bit */
> + __u32 flags;
> + __u32 noi; /* Number of interrupts */
> + __u8 isc; /* Guest interrupt subclass */
> + __u8 sbo; /* Offset of guest summary bit vector */
> + __u16 pad;
> + } reg_aen;
> + __u64 reserved[8];
> + } u;
> +};
> +
> +/* types for kvm_s390_zpci_op->op */
> +#define KVM_S390_ZPCIOP_REG_AEN 0
> +#define KVM_S390_ZPCIOP_DEREG_AEN 1
> +
> +/* flags for kvm_s390_zpci_op->u.reg_aen.flags */
> +#define KVM_S390_ZPCIOP_REGAEN_HOST (1 << 0)
> +
> #endif /* __LINUX_KVM_H */

Thomas