[v3,16/17] KVM: introduce a KVM_DESTROY_DEVICE ioctl

The 'destroy' method is currently used to destroy all devices when the
VM is destroyed after the vCPUs have been freed.

This new KVM ioctl exposes the same KVM device method. It acts as a
software reset of the VM to 'destroy' selected devices when necessary
and perform the required cleanups on the vCPUs. Called with the
kvm->lock.

The 'destroy' method could be improved by returning an error code.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
---

  Changes since v2 :

 - checked that device is owned by VM
 
 include/uapi/linux/kvm.h          |  7 ++++++
 virt/kvm/kvm_main.c               | 42 +++++++++++++++++++++++++++++++
 Documentation/virtual/kvm/api.txt | 20 +++++++++++++++
 3 files changed, 69 insertions(+)

On Fri, Mar 15, 2019 at 01:06:08PM +0100, Cédric Le Goater wrote:
> The 'destroy' method is currently used to destroy all devices when the
> VM is destroyed after the vCPUs have been freed.
> 
> This new KVM ioctl exposes the same KVM device method. It acts as a
> software reset of the VM to 'destroy' selected devices when necessary
> and perform the required cleanups on the vCPUs. Called with the
> kvm->lock.
> 
> The 'destroy' method could be improved by returning an error code.
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Cédric Le Goater <clg@kaod.org>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
> 
>   Changes since v2 :
> 
>  - checked that device is owned by VM
>  
>  include/uapi/linux/kvm.h          |  7 ++++++
>  virt/kvm/kvm_main.c               | 42 +++++++++++++++++++++++++++++++
>  Documentation/virtual/kvm/api.txt | 20 +++++++++++++++
>  3 files changed, 69 insertions(+)
> 
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 52bf74a1616e..d78fafa54274 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1183,6 +1183,11 @@ struct kvm_create_device {
>  	__u32	flags;	/* in: KVM_CREATE_DEVICE_xxx */
>  };
>  
> +struct kvm_destroy_device {
> +	__u32	fd;	/* in: device handle */
> +	__u32	flags;	/* in: unused */
> +};
> +
>  struct kvm_device_attr {
>  	__u32	flags;		/* no flags currently defined */
>  	__u32	group;		/* device-defined */
> @@ -1331,6 +1336,8 @@ struct kvm_s390_ucas_mapping {
>  #define KVM_GET_DEVICE_ATTR	  _IOW(KVMIO,  0xe2, struct kvm_device_attr)
>  #define KVM_HAS_DEVICE_ATTR	  _IOW(KVMIO,  0xe3, struct kvm_device_attr)
>  
> +#define KVM_DESTROY_DEVICE	  _IOWR(KVMIO,  0xf0, struct kvm_destroy_device)
> +
>  /*
>   * ioctls for vcpu fds
>   */
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index e4881a8c2a6f..7b616a1d48cf 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -3026,6 +3026,34 @@ static int kvm_ioctl_create_device(struct kvm *kvm,
>  	return 0;
>  }
>  
> +static int kvm_ioctl_destroy_device(struct kvm *kvm,
> +				    struct kvm_destroy_device *dd)
> +{
> +	struct fd f;
> +	struct kvm_device *dev;
> +
> +	f = fdget(dd->fd);
> +	if (!f.file)
> +		return -EBADF;
> +
> +	dev = kvm_device_from_filp(f.file);
> +	fdput(f);
> +
> +	if (!dev)
> +		return -ENODEV;
> +
> +	if (dev->kvm != kvm)
> +		return -EPERM;
> +
> +	mutex_lock(&kvm->lock);
> +	list_del(&dev->vm_node);
> +	dev->ops->destroy(dev);
> +	mutex_unlock(&kvm->lock);
> +
> +	/* TODO: kvm_put_kvm() crashes the host on some occasion ? */
> +	return 0;
> +}
> +
>  static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
>  {
>  	switch (arg) {
> @@ -3270,6 +3298,20 @@ static long kvm_vm_ioctl(struct file *filp,
>  		r = 0;
>  		break;
>  	}
> +	case KVM_DESTROY_DEVICE: {
> +		struct kvm_destroy_device dd;
> +
> +		r = -EFAULT;
> +		if (copy_from_user(&dd, argp, sizeof(dd)))
> +			goto out;
> +
> +		r = kvm_ioctl_destroy_device(kvm, &dd);
> +		if (r)
> +			goto out;
> +
> +		r = 0;
> +		break;
> +	}
>  	case KVM_CHECK_EXTENSION:
>  		r = kvm_vm_ioctl_check_extension_generic(kvm, arg);
>  		break;
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index 1db1435769b4..914471494602 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -3857,6 +3857,26 @@ number of valid entries in the 'entries' array, which is then filled.
>  'index' and 'flags' fields in 'struct kvm_cpuid_entry2' are currently reserved,
>  userspace should not expect to get any particular value there.
>  
> +4.119 KVM_DESTROY_DEVICE
> +
> +Capability: KVM_CAP_DEVICE_CTRL
> +Type: vm ioctl
> +Parameters: struct kvm_destroy_device (in)
> +Returns: 0 on success, -1 on error
> +Errors:
> +  ENODEV: The device type is unknown or unsupported
> +  EPERM: The device does not belong to the VM
> +
> +  Other error conditions may be defined by individual device types or
> +  have their standard meanings.
> +
> +Destroys an emulated device in the kernel.
> +
> +struct kvm_destroy_device {
> +	__u32	fd;	/* in: device handle */
> +	__u32	flags;	/* unused */
> +};
> +
>  5. The kvm_run structure
>  ------------------------
>