Re: [PATCH v3 3/6] vduse: add vq group support

Jason Wang
2025-09-24T01:10:38Z

On Mon, Sep 22, 2025 at 6:51 PM Eugenio Perez Martin
<eperezma@redhat.com> wrote:
>
> On Mon, Sep 22, 2025 at 3:16 AM Jason Wang <jasowang@redhat.com> wrote:
> >
> > On Fri, Sep 19, 2025 at 5:34 PM Eugenio Pérez <eperezma@redhat.com> wrote:
> > >
> > > This allows sepparate the different virtqueues in groups that shares the
> > > same address space. Asking the VDUSE device for the groups of the vq at
> > > the beginning as they're needed for the DMA API.
> > >
> > > Allocating 3 vq groups as net is the device that need the most groups:
> > > * Dataplane (guest passthrough)
> > > * CVQ
> > > * Shadowed vrings.
> > >
> > > Future versions of the series can include dynamic allocation of the
> > > groups array so VDUSE can declare more groups.
> > >
> > > Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> > > ---
> > > v3:
> > > * Make the default group an invalid group as long as VDUSE device does
> > > not set it to some valid u32 value. Modify the vdpa core to take that
> > > into account (Jason).
> > > * Create the VDUSE_DEV_MAX_GROUPS instead of using a magic number
> > >
> > > v2:
> > > * Now the vq group is in vduse_vq_config struct instead of issuing one
> > > VDUSE message per vq.
> > >
> > > v1:
> > > * Fix: Remove BIT_ULL(VIRTIO_S_*), as _S_ is already the bit (Maxime)
> > >
> > > RFC v3:
> > > * Increase VDUSE_MAX_VQ_GROUPS to 0xffff (Jason). It was set to a lower
> > > value to reduce memory consumption, but vqs are already limited to
> > > that value and userspace VDUSE is able to allocate that many vqs.
> > > * Remove the descs vq group capability as it will not be used and we can
> > > add it on top.
> > > * Do not ask for vq groups in number of vq groups < 2.
> > > * Move the valid vq groups range check to vduse_validate_config.
> > >
> > > RFC v2:
> > > * Cache group information in kernel, as we need to provide the vq map
> > > tokens properly.
> > > * Add descs vq group to optimize SVQ forwarding and support indirect
> > > descriptors out of the box.
> > > ---
> > > drivers/vdpa/ifcvf/ifcvf_main.c | 2 +-
> > > drivers/vdpa/mlx5/net/mlx5_vnet.c | 2 +-
> > > drivers/vdpa/vdpa_sim/vdpa_sim.c | 2 +-
> > > drivers/vdpa/vdpa_user/vduse_dev.c | 51 +++++++++++++++++++++++++++---
> > > drivers/vhost/vdpa.c | 11 +++++--
> > > include/linux/vdpa.h | 5 +--
> > > include/uapi/linux/vduse.h | 12 +++++--
> > > 7 files changed, 69 insertions(+), 16 deletions(-)
> > >
> > > diff --git a/drivers/vdpa/ifcvf/ifcvf_main.c b/drivers/vdpa/ifcvf/ifcvf_main.c
> > > index 6658dc74d915..ea6643760fb7 100644
> > > --- a/drivers/vdpa/ifcvf/ifcvf_main.c
> > > +++ b/drivers/vdpa/ifcvf/ifcvf_main.c
> > > @@ -559,7 +559,7 @@ static size_t ifcvf_vdpa_get_config_size(struct vdpa_device *vdpa_dev)
> > > return vf->config_size;
> > > }
> > >
> > > -static u32 ifcvf_vdpa_get_vq_group(struct vdpa_device *vdpa, u16 idx)
> > > +static s64 ifcvf_vdpa_get_vq_group(struct vdpa_device *vdpa, u16 idx)
> > > {
> > > return 0;
> > > }
> > > diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > index 82034efb74fc..daab0ccb78b2 100644
> > > --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > @@ -2640,7 +2640,7 @@ static u32 mlx5_vdpa_get_vq_align(struct vdpa_device *vdev)
> > > return PAGE_SIZE;
> > > }
> > >
> > > -static u32 mlx5_vdpa_get_vq_group(struct vdpa_device *vdev, u16 idx)
> > > +static s64 mlx5_vdpa_get_vq_group(struct vdpa_device *vdev, u16 idx)
> > > {
> > > struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
> > >
> > > diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > > index c1c6431950e1..fe4d65aaf6aa 100644
> > > --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > > +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > > @@ -412,7 +412,7 @@ static u32 vdpasim_get_vq_align(struct vdpa_device *vdpa)
> > > return VDPASIM_QUEUE_ALIGN;
> > > }
> > >
> > > -static u32 vdpasim_get_vq_group(struct vdpa_device *vdpa, u16 idx)
> > > +static s64 vdpasim_get_vq_group(struct vdpa_device *vdpa, u16 idx)
> > > {
> > > /* RX and TX belongs to group 0, CVQ belongs to group 1 */
> > > if (idx == 2)
> > > diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > index 2b6a8958ffe0..7ddd81456f7b 100644
> > > --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> > > +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > @@ -40,6 +40,7 @@
> > > #define DRV_LICENSE "GPL v2"
> > >
> > > #define VDUSE_DEV_MAX (1U << MINORBITS)
> > > +#define VDUSE_DEV_MAX_GROUPS 0xffff
> > > #define VDUSE_MAX_BOUNCE_SIZE (1024 * 1024 * 1024)
> > > #define VDUSE_MIN_BOUNCE_SIZE (1024 * 1024)
> > > #define VDUSE_BOUNCE_SIZE (64 * 1024 * 1024)
> > > @@ -49,6 +50,8 @@
> > >
> > > #define IRQ_UNBOUND -1
> > >
> > > +#define VQ_GROUP_INVALID -1
> > > +
> > > struct vduse_virtqueue {
> > > u16 index;
> > > u16 num_max;
> > > @@ -59,6 +62,7 @@ struct vduse_virtqueue {
> > > struct vdpa_vq_state state;
> > > bool ready;
> > > bool kicked;
> > > + u32 vq_group;
> > > spinlock_t kick_lock;
> > > spinlock_t irq_lock;
> > > struct eventfd_ctx *kickfd;
> > > @@ -115,6 +119,7 @@ struct vduse_dev {
> > > u8 status;
> > > u32 vq_num;
> > > u32 vq_align;
> > > + u32 ngroups;
> > > struct vduse_umem *umem;
> > > struct mutex mem_lock;
> > > unsigned int bounce_size;
> > > @@ -456,6 +461,7 @@ static void vduse_dev_reset(struct vduse_dev *dev)
> > > vq->driver_addr = 0;
> > > vq->device_addr = 0;
> > > vq->num = 0;
> > > + vq->vq_group = VQ_GROUP_INVALID;
> > > memset(&vq->state, 0, sizeof(vq->state));
> > >
> > > spin_lock(&vq->kick_lock);
> > > @@ -593,6 +599,19 @@ static int vduse_vdpa_set_vq_state(struct vdpa_device *vdpa, u16 idx,
> > > return 0;
> > > }
> > >
> > > +static s64 vduse_get_vq_group(struct vdpa_device *vdpa, u16 idx)
> > > +{
> > > + struct vduse_dev *dev = vdpa_to_vduse(vdpa);
> > > +
> > > + if (dev->api_version < VDUSE_API_VERSION_1)
> > > + return 0;
> > > +
> > > + if (dev->vqs[idx]->vq_group == VQ_GROUP_INVALID)
> > > + return -EINVAL;
> > > +
> > > + return dev->vqs[idx]->vq_group;
> > > +}
> > > +
> > > static int vduse_vdpa_get_vq_state(struct vdpa_device *vdpa, u16 idx,
> > > struct vdpa_vq_state *state)
> > > {
> > > @@ -790,6 +809,7 @@ static const struct vdpa_config_ops vduse_vdpa_config_ops = {
> > > .set_vq_cb = vduse_vdpa_set_vq_cb,
> > > .set_vq_num = vduse_vdpa_set_vq_num,
> > > .get_vq_size = vduse_vdpa_get_vq_size,
> > > + .get_vq_group = vduse_get_vq_group,
> > > .set_vq_ready = vduse_vdpa_set_vq_ready,
> > > .get_vq_ready = vduse_vdpa_get_vq_ready,
> > > .set_vq_state = vduse_vdpa_set_vq_state,
> > > @@ -1253,12 +1273,24 @@ static long vduse_dev_ioctl(struct file *file, unsigned int cmd,
> > > if (config.index >= dev->vq_num)
> > > break;
> > >
> > > - if (!is_mem_zero((const char *)config.reserved,
> > > - sizeof(config.reserved)))
> > > + if (dev->api_version < VDUSE_API_VERSION_1 && config.group)
> > > + break;
> > > +
> > > + if (dev->api_version >= VDUSE_API_VERSION_1) {
> > > + if (config.group > dev->ngroups)
> > > + break;
> > > + if (dev->status & VIRTIO_CONFIG_S_DRIVER_OK)
> > > + break;
> >
> > This seems to be a new requirement for V1. Please explain why.
> >
>
> Would a code comment like "The device is not allowed to change the VQ
> group after the driver sets DRIVER_OK" work? I'm tempted to add "VQ
> group or size", but it was not an error previously so I'm ok with
> leaving it only for vq groups.

That's fine but I wonder why we check DRIVER_OK instead of FEATURES_OK.

>
> > > + }
> > > +
> > > + if (config.reserved1 ||
> > > + !is_mem_zero((const char *)config.reserved2,
> > > + sizeof(config.reserved2)))
> > > break;
> > >
> > > index = array_index_nospec(config.index, dev->vq_num);
> > > dev->vqs[index]->num_max = config.max_size;
> > > + dev->vqs[index]->vq_group = config.group;
> > > ret = 0;
> > > break;
> > > }
> > > @@ -1738,12 +1770,20 @@ static bool features_is_valid(struct vduse_dev_config *config)
> > > return true;
> > > }
> > >
> > > -static bool vduse_validate_config(struct vduse_dev_config *config)
> > > +static bool vduse_validate_config(struct vduse_dev_config *config,
> > > + u64 api_version)
> > > {
> > > if (!is_mem_zero((const char *)config->reserved,
> > > sizeof(config->reserved)))
> > > return false;
> > >
> > > + if (api_version < VDUSE_API_VERSION_1 && config->ngroups)
> > > + return false;
> > > +
> > > + if (api_version >= VDUSE_API_VERSION_1 &&
> > > + config->ngroups > VDUSE_DEV_MAX_GROUPS)
> > > + return false;
> > > +
> > > if (config->vq_align > PAGE_SIZE)
> > > return false;
> > >
> > > @@ -1859,6 +1899,7 @@ static int vduse_create_dev(struct vduse_dev_config *config,
> > > dev->device_features = config->features;
> > > dev->device_id = config->device_id;
> > > dev->vendor_id = config->vendor_id;
> > > + dev->ngroups = (dev->api_version < 1) ? 1 : (config->ngroups ?: 1);
> >
> > Should we fail if config->ngroups is zero when version is 1?
> >
>
> The devices that don't need to mess with vq groups are better with not
> needing to know anything about it in their codebases, in my opinion.
> Having to learn about what is a vq group for a newcomer to vDPA/VDUSE
> is setting the barrier higher for little benefit.
>
> We can obtain the same advantage of reserving the value 0 with a new
> API version or VDUSE feature flags.
>
> Having said that, I'm ok if you prefer this device creation to fail in
> that case.

I prefer to fail in this case.

>
> > > dev->name = kstrdup(config->name, GFP_KERNEL);
> > > if (!dev->name)
> > > goto err_str;
> > > @@ -1937,7 +1978,7 @@ static long vduse_ioctl(struct file *file, unsigned int cmd,
> > > break;
> > >
> > > ret = -EINVAL;
> > > - if (vduse_validate_config(&config) == false)
> > > + if (!vduse_validate_config(&config, control->api_version))
> > > break;
> > >
> > > buf = vmemdup_user(argp + size, config.config_size);
> > > @@ -2018,7 +2059,7 @@ static int vduse_dev_init_vdpa(struct vduse_dev *dev, const char *name)
> > >
> > > vdev = vdpa_alloc_device(struct vduse_vdpa, vdpa, dev->dev,
> > > &vduse_vdpa_config_ops, &vduse_map_ops,
> > > - 1, 1, name, true);
> > > + dev->ngroups, 1, name, true);
> > > if (IS_ERR(vdev))
> > > return PTR_ERR(vdev);
> > >
> > > diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> > > index 05a481e4c385..6305382eacbb 100644
> > > --- a/drivers/vhost/vdpa.c
> > > +++ b/drivers/vhost/vdpa.c
> > > @@ -22,6 +22,7 @@
> > > #include <linux/vdpa.h>
> > > #include <linux/nospec.h>
> > > #include <linux/vhost.h>
> > > +#include <linux/types.h>
> > >
> > > #include "vhost.h"
> > >
> > > @@ -657,16 +658,20 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
> > > return -EFAULT;
> > > ops->set_vq_ready(vdpa, idx, s.num);
> > > return 0;
> > > - case VHOST_VDPA_GET_VRING_GROUP:
> > > + case VHOST_VDPA_GET_VRING_GROUP: {
> > > + u64 group;
> > > +
> > > if (!ops->get_vq_group)
> > > return -EOPNOTSUPP;
> > > s.index = idx;
> > > - s.num = ops->get_vq_group(vdpa, idx);
> > > - if (s.num >= vdpa->ngroups)
> > > + group = ops->get_vq_group(vdpa, idx);
> > > + if (group >= vdpa->ngroups || group > U32_MAX || group < 0)
> > > return -EIO;
> > > else if (copy_to_user(argp, &s, sizeof(s)))
> > > return -EFAULT;
> > > + s.num = group;
> > > return 0;
> > > + }
> > > case VHOST_VDPA_GET_VRING_DESC_GROUP:
> > > if (!vhost_vdpa_has_desc_group(v))
> > > return -EOPNOTSUPP;
> > > diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
> > > index 4cf21d6e9cfd..76a673ef7deb 100644
> > > --- a/include/linux/vdpa.h
> > > +++ b/include/linux/vdpa.h
> > > @@ -211,7 +211,8 @@ struct vdpa_map_file {
> > > * virtqueue (optional)
> > > * @vdev: vdpa device
> > > * @idx: virtqueue index
> > > - * Returns u32: group id for this virtqueue
> > > + * Returns i64: (32 bits wide) group id for this
> >
> > Let's separate the u32->s64 changes. And maybe it's fine to say
> > returns s64 and explain U32_MAX is the maximum value allowed.
> >
>
> Sure, sending a new version with that.
>
> > > + * virtqueue if >0. If <0, errno.
> > > * @get_vq_desc_group: Get the group id for the descriptor table of
> > > * a specific virtqueue (optional)
> > > * @vdev: vdpa device
> > > @@ -398,7 +399,7 @@ struct vdpa_config_ops {
> > >
> > > /* Device ops */
> > > u32 (*get_vq_align)(struct vdpa_device *vdev);
> > > - u32 (*get_vq_group)(struct vdpa_device *vdev, u16 idx);
> > > + s64 (*get_vq_group)(struct vdpa_device *vdev, u16 idx);
> > > u32 (*get_vq_desc_group)(struct vdpa_device *vdev, u16 idx);
> > > u64 (*get_device_features)(struct vdpa_device *vdev);
> > > u64 (*get_backend_features)(const struct vdpa_device *vdev);
> > > diff --git a/include/uapi/linux/vduse.h b/include/uapi/linux/vduse.h
> > > index ccb92a1efce0..a3d51cf6df3a 100644
> > > --- a/include/uapi/linux/vduse.h
> > > +++ b/include/uapi/linux/vduse.h
> > > @@ -31,6 +31,7 @@
> > > * @features: virtio features
> > > * @vq_num: the number of virtqueues
> > > * @vq_align: the allocation alignment of virtqueue's metadata
> > > + * @ngroups: number of vq groups that VDUSE device declares
> > > * @reserved: for future use, needs to be initialized to zero
> > > * @config_size: the size of the configuration space
> > > * @config: the buffer of the configuration space
> > > @@ -45,7 +46,8 @@ struct vduse_dev_config {
> > > __u64 features;
> > > __u32 vq_num;
> > > __u32 vq_align;
> > > - __u32 reserved[13];
> > > + __u32 ngroups; /* if VDUSE_API_VERSION >= 1 */
> > > + __u32 reserved[12];
> > > __u32 config_size;
> > > __u8 config[];
> > > };
> > > @@ -122,14 +124,18 @@ struct vduse_config_data {
> > > * struct vduse_vq_config - basic configuration of a virtqueue
> > > * @index: virtqueue index
> > > * @max_size: the max size of virtqueue
> > > - * @reserved: for future use, needs to be initialized to zero
> > > + * @reserved1: for future use, needs to be initialized to zero
> > > + * @group: virtqueue group
> > > + * @reserved2: for future use, needs to be initialized to zero
> > > *
> > > * Structure used by VDUSE_VQ_SETUP ioctl to setup a virtqueue.
> > > */
> > > struct vduse_vq_config {
> > > __u32 index;
> > > __u16 max_size;
> > > - __u16 reserved[13];
> > > + __u16 reserved1;
> > > + __u32 group;
> > > + __u16 reserved2[10];
> > > };
> > >
> > > /*
> > > --
> > > 2.51.0
> > >
> >
> > Thanks
> >
>

Thanks