Subject: Re: [PATCH v2 15/16] KVM: introduce a KVM_DESTROY_DEVICE ioctl

From: David Gibson <[email-masked]>
Date: Mon, 25 Feb 2019 15:15:07 +1100

On Fri, Feb 22, 2019 at 12:28:39PM +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.
> 
> Signed-off-by: Cédric Le Goater <[email-masked]>

Again, has this been discussed with Paolo and/or other KVM core
people?

> ---
>  include/uapi/linux/kvm.h          |  7 ++++++
>  virt/kvm/kvm_main.c               | 38 +++++++++++++++++++++++++++++++
>  Documentation/virtual/kvm/api.txt | 19 ++++++++++++++++
>  3 files changed, 64 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 84717d8cb5e4..983d5c37f710 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -3026,6 +3026,30 @@ 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;

Don't you need to verify that the device belongs to this KVM instance?

> +	mutex_lock(&kvm->lock);
> +	list_del(&dev->vm_node);
> +	dev->ops->destroy(dev);
> +	mutex_unlock(&kvm->lock);
> +
> +	return 0;
> +}
> +
>  static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
>  {
>  	switch (arg) {
> @@ -3270,6 +3294,20 @@ 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..c2ba18279298 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -3857,6 +3857,25 @@ 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
> +
> +  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
>  ------------------------
>  

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson