[PATCH] vhost/vsock: add IOTLB API support

Stefano Garzarella
2020-10-29T17:44:15Z

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

[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 = {
--
2.26.2