Re: [PATCH] vhost/vsock: add IOTLB API support

[Jason Wang <jasowang@redhat.com>]

On 2020/10/30 上午1:43, Stefano Garzarella wrote:
> This patch enables the IOTLB API support for vhost-vsock devices,
> allowing the userspace to emulate an IOMMU for the guest.
>
> These changes were made following vhost-net, in details this patch:
> - exposes VIRTIO_F_ACCESS_PLATFORM feature and inits the iotlb
>    device if the feature is acked
> - implements VHOST_GET_BACKEND_FEATURES and
>    VHOST_SET_BACKEND_FEATURES ioctls
> - calls vq_meta_prefetch() before vq processing to prefetch vq
>    metadata address in IOTLB
> - provides .read_iter, .write_iter, and .poll callbacks for the
>    chardev; they are used by the userspace to exchange IOTLB messages
>
> This patch was tested with QEMU and a patch applied [1] to fix a
> simple issue:
>      $ qemu -M q35,accel=kvm,kernel-irqchip=split \
>             -drive file=fedora.qcow2,format=qcow2,if=virtio \
>             -device intel-iommu,intremap=on \
>             -device vhost-vsock-pci,guest-cid=3,iommu_platform=on


Patch looks good, but a question:

It looks to me you don't enable ATS which means vhost won't get any 
invalidation request or did I miss anything?

Thanks


>
> [1] https://lists.gnu.org/archive/html/qemu-devel/2020-10/msg09077.html
>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
>   drivers/vhost/vsock.c | 68 +++++++++++++++++++++++++++++++++++++++++--
>   1 file changed, 65 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index a483cec31d5c..5e78fb719602 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -30,7 +30,12 @@
>   #define VHOST_VSOCK_PKT_WEIGHT 256
>   
>   enum {
> -	VHOST_VSOCK_FEATURES = VHOST_FEATURES,
> +	VHOST_VSOCK_FEATURES = VHOST_FEATURES |
> +			       (1ULL << VIRTIO_F_ACCESS_PLATFORM)
> +};
> +
> +enum {
> +	VHOST_VSOCK_BACKEND_FEATURES = (1ULL << VHOST_BACKEND_F_IOTLB_MSG_V2)
>   };
>   
>   /* Used to track all the vhost_vsock instances on the system. */
> @@ -94,6 +99,9 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
>   	if (!vhost_vq_get_backend(vq))
>   		goto out;
>   
> +	if (!vq_meta_prefetch(vq))
> +		goto out;
> +
>   	/* Avoid further vmexits, we're already processing the virtqueue */
>   	vhost_disable_notify(&vsock->dev, vq);
>   
> @@ -449,6 +457,9 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work *work)
>   	if (!vhost_vq_get_backend(vq))
>   		goto out;
>   
> +	if (!vq_meta_prefetch(vq))
> +		goto out;
> +
>   	vhost_disable_notify(&vsock->dev, vq);
>   	do {
>   		u32 len;
> @@ -766,8 +777,12 @@ static int vhost_vsock_set_features(struct vhost_vsock *vsock, u64 features)
>   	mutex_lock(&vsock->dev.mutex);
>   	if ((features & (1 << VHOST_F_LOG_ALL)) &&
>   	    !vhost_log_access_ok(&vsock->dev)) {
> -		mutex_unlock(&vsock->dev.mutex);
> -		return -EFAULT;
> +		goto err;
> +	}
> +
> +	if ((features & (1ULL << VIRTIO_F_ACCESS_PLATFORM))) {
> +		if (vhost_init_device_iotlb(&vsock->dev, true))
> +			goto err;
>   	}
>   
>   	for (i = 0; i < ARRAY_SIZE(vsock->vqs); i++) {
> @@ -778,6 +793,10 @@ static int vhost_vsock_set_features(struct vhost_vsock *vsock, u64 features)
>   	}
>   	mutex_unlock(&vsock->dev.mutex);
>   	return 0;
> +
> +err:
> +	mutex_unlock(&vsock->dev.mutex);
> +	return -EFAULT;
>   }
>   
>   static long vhost_vsock_dev_ioctl(struct file *f, unsigned int ioctl,
> @@ -811,6 +830,18 @@ static long vhost_vsock_dev_ioctl(struct file *f, unsigned int ioctl,
>   		if (copy_from_user(&features, argp, sizeof(features)))
>   			return -EFAULT;
>   		return vhost_vsock_set_features(vsock, features);
> +	case VHOST_GET_BACKEND_FEATURES:
> +		features = VHOST_VSOCK_BACKEND_FEATURES;
> +		if (copy_to_user(argp, &features, sizeof(features)))
> +			return -EFAULT;
> +		return 0;
> +	case VHOST_SET_BACKEND_FEATURES:
> +		if (copy_from_user(&features, argp, sizeof(features)))
> +			return -EFAULT;
> +		if (features & ~VHOST_VSOCK_BACKEND_FEATURES)
> +			return -EOPNOTSUPP;
> +		vhost_set_backend_features(&vsock->dev, features);
> +		return 0;
>   	default:
>   		mutex_lock(&vsock->dev.mutex);
>   		r = vhost_dev_ioctl(&vsock->dev, ioctl, argp);
> @@ -823,6 +854,34 @@ static long vhost_vsock_dev_ioctl(struct file *f, unsigned int ioctl,
>   	}
>   }
>   
> +static ssize_t vhost_vsock_chr_read_iter(struct kiocb *iocb, struct iov_iter *to)
> +{
> +	struct file *file = iocb->ki_filp;
> +	struct vhost_vsock *vsock = file->private_data;
> +	struct vhost_dev *dev = &vsock->dev;
> +	int noblock = file->f_flags & O_NONBLOCK;
> +
> +	return vhost_chr_read_iter(dev, to, noblock);
> +}
> +
> +static ssize_t vhost_vsock_chr_write_iter(struct kiocb *iocb,
> +					struct iov_iter *from)
> +{
> +	struct file *file = iocb->ki_filp;
> +	struct vhost_vsock *vsock = file->private_data;
> +	struct vhost_dev *dev = &vsock->dev;
> +
> +	return vhost_chr_write_iter(dev, from);
> +}
> +
> +static __poll_t vhost_vsock_chr_poll(struct file *file, poll_table *wait)
> +{
> +	struct vhost_vsock *vsock = file->private_data;
> +	struct vhost_dev *dev = &vsock->dev;
> +
> +	return vhost_chr_poll(file, dev, wait);
> +}
> +
>   static const struct file_operations vhost_vsock_fops = {
>   	.owner          = THIS_MODULE,
>   	.open           = vhost_vsock_dev_open,
> @@ -830,6 +889,9 @@ static const struct file_operations vhost_vsock_fops = {
>   	.llseek		= noop_llseek,
>   	.unlocked_ioctl = vhost_vsock_dev_ioctl,
>   	.compat_ioctl   = compat_ptr_ioctl,
> +	.read_iter      = vhost_vsock_chr_read_iter,
> +	.write_iter     = vhost_vsock_chr_write_iter,
> +	.poll           = vhost_vsock_chr_poll,
>   };
>   
>   static struct miscdevice vhost_vsock_misc = {