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

[Matthew Rosato <mjrosato@linux.ibm.com>]

On 5/16/22 5:52 AM, Thomas Huth wrote:
> 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?

Yup, VM ioctl, bad copy/paste job...

> 
>> +: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?
> 

Oh no, this is a leftover from a prior version...  Good catch.  There 
should no longer be a copy_to_user.

>> +    __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?

It's a VM ioctl.  These are guest kernel physical addresses that are 
later pinned in arch/s390/kvm/pci.c:kvm_s390_pci_aif_enable() as part of 
handling the ioctl.

> 
>> +            __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?

Sure, I can mention them.  And yes, I agree that userspace should 
initialize them to 0, I'll update the QEMU series accordingly.

> 
>>   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?

copy_to_user should be dropped.  Thanks!

> 
>> +        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).

Good idea, will do

> 
>> +        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). >

As mentioned above, the copy_to_user() should be removed.

>> +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
>