Message-ID: <CACGkMEtUv7Kge4A6rcSSiVu4moi5vSNU97pQ7_LiUmprOb0wBw@mail.gmail.com>
Date: Thu, 15 Jan 2026 16:41:05 +0800
From: Jason Wang <jasowang@...hat.com>
To: Eugenio Pérez <eperezma@...hat.com>
Cc: "Michael S . Tsirkin" <mst@...hat.com>, Maxime Coquelin <mcoqueli@...hat.com>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, virtualization@...ts.linux.dev, 
	Stefano Garzarella <sgarzare@...hat.com>, Yongji Xie <xieyongji@...edance.com>, 
	linux-kernel@...r.kernel.org, Cindy Lu <lulu@...hat.com>, 
	Laurent Vivier <lvivier@...hat.com>
Subject: Re: [PATCH v12 11/13] vduse: add vq group asid support

On Thu, Jan 15, 2026 at 2:49 AM Eugenio Pérez <eperezma@...hat.com> wrote:
>
> Add support for assigning Address Space Identifiers (ASIDs) to each VQ
> group.  This enables mapping each group into a distinct memory space.
>
> The vq group to ASID association is protected by a rwlock now.  But the
> mutex domain_lock keeps protecting the domains of all ASIDs, as some
> operations like the one related with the bounce buffer size still
> requires to lock all the ASIDs.
>
> Signed-off-by: Eugenio Pérez <eperezma@...hat.com>
>
> ---
> Future improvements can include performance optimizations on top like
> ore to RCU or thread synchronized atomics, or hardening by tracking ASID
> or ASID hashes on unused bits of the DMA address.
>
> Tested virtio_vdpa by adding manually two threads in vduse_set_status:
> one of them modifies the vq group 0 ASID and the other one map and unmap
> memory continuously.  After a while, the two threads stop and the usual
> work continues.  Test with version 0, version 1 with the old ioctl, and
> version 1 with the new ioctl.
>
> Tested with vhost_vdpa by migrating a VM while ping on OVS+VDUSE.  A few
> workaround were needed in some parts:
> * Do not enable CVQ before data vqs in QEMU, as VDUSE does not forward
>   the enable message to the userland device.  This will be solved in the
>   future.
> * Share the suspended state between all vhost devices in QEMU:
>   https://lists.nongnu.org/archive/html/qemu-devel/2025-11/msg02947.html
> * Implement a fake VDUSE suspend vdpa operation callback that always
>   returns true in the kernel.  DPDK suspend the device at the first
>   GET_VRING_BASE.
> * Remove the CVQ blocker in ASID.
>
> The driver vhost_vdpa was also tested with version 0, version 1 with the
> old ioctl, version 1 with the new ioctl but only one ASID, and version 1
> with many ASID.
>
> ---
> v12:
> * Using scoped guards for vq group rwlock, so the one queue optimization
>   is not missed (Jason proposed to factor them into helpers).
> * Add the _v2 suffix to vduse_iova_range_v2 struct name fixing the doc
>   (MST).
> * s/verion/version/ in patch message.
> * Remove trailing ; after a comment (Jason).
>
> v11:
> * Remove duplicated free_pages_exact in vduse_domain_free_coherent
>   (Jason).
> * Do not take the vq groups lock if nas == 1.
> * Do not reset the vq group ASID in vq reset (Jason).  Removed extra
>   function vduse_set_group_asid_nomsg, not needed anymore.
> * Move the vduse_iotlb_entry_v2 argument to a new ioctl, as argument
>   didn't match the previous VDUSE_IOTLB_GET_FD.
> * Move the asid < dev->nas check to vdpa core.
>
> v10:
> * Back to rwlock version so stronger locks are used.
> * Take out allocations from rwlock.
> * Forbid changing ASID of a vq group after DRIVER_OK (Jason)
> * Remove bad fetching again of domain variable in
>   vduse_dev_max_mapping_size (Yongji).
> * Remove unused vdev definition in vdpa map_ops callbacks (kernel test
>   robot).
>
> v9:
> * Replace mutex with rwlock, as the vdpa map_ops can run from atomic
>   context.
>
> v8:
> * Revert the mutex to rwlock change, it needs proper profiling to
>   justify it.
>
> v7:
> * Take write lock in the error path (Jason).
>
> v6:
> * Make vdpa_dev_add use gotos for error handling (MST).
> * s/(dev->api_version < 1) ?/(dev->api_version < VDUSE_API_VERSION_1) ?/
>   (MST).
> * Fix struct name not matching in the doc.
>
> v5:
> * Properly return errno if copy_to_user returns >0 in VDUSE_IOTLB_GET_FD
>   ioctl (Jason).
> * Properly set domain bounce size to divide equally between nas (Jason).
> * Exclude "padding" member from the only >V1 members in
>   vduse_dev_request.
>
> v4:
> * Divide each domain bounce size between the device bounce size (Jason).
> * revert unneeded addr = NULL assignment (Jason)
> * Change if (x && (y || z)) return to if (x) { if (y) return; if (z)
>   return; } (Jason)
> * Change a bad multiline comment, using @ caracter instead of * (Jason).
> * Consider config->nas == 0 as a fail (Jason).
>
> v3:
> * Get the vduse domain through the vduse_as in the map functions
>   (Jason).
> * Squash with the patch creating the vduse_as struct (Jason).
> * Create VDUSE_DEV_MAX_AS instead of comparing agains a magic number
>   (Jason)
>
> v2:
> * Convert the use of mutex to rwlock.
>
> 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 TODO about merging VDUSE_IOTLB_GET_FD ioctl with
>   VDUSE_IOTLB_GET_INFO.
> * Use of array_index_nospec in VDUSE device ioctls.
> * Embed vduse_iotlb_entry into vduse_iotlb_entry_v2.
> * Move the umem mutex to asid struct so there is no contention between
>   ASIDs.
>
> RFC v2:
> * Make iotlb entry the last one of vduse_iotlb_entry_v2 so the first
>   part of the struct is the same.
> ---
>  drivers/vdpa/vdpa_user/vduse_dev.c | 385 +++++++++++++++++++----------
>  include/uapi/linux/vduse.h         |  63 ++++-
>  2 files changed, 312 insertions(+), 136 deletions(-)
>
> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> index d658f3e1cebf..2727c0c26003 100644
> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> @@ -9,6 +9,7 @@
>   */
>
>  #include "linux/virtio_net.h"
> +#include <linux/cleanup.h>
>  #include <linux/init.h>
>  #include <linux/module.h>
>  #include <linux/cdev.h>
> @@ -41,6 +42,7 @@
>
>  #define VDUSE_DEV_MAX (1U << MINORBITS)
>  #define VDUSE_DEV_MAX_GROUPS 0xffff
> +#define VDUSE_DEV_MAX_AS 0xffff
>  #define VDUSE_MAX_BOUNCE_SIZE (1024 * 1024 * 1024)
>  #define VDUSE_MIN_BOUNCE_SIZE (1024 * 1024)
>  #define VDUSE_BOUNCE_SIZE (64 * 1024 * 1024)
> @@ -86,7 +88,15 @@ struct vduse_umem {
>         struct mm_struct *mm;
>  };
>
> +struct vduse_as {
> +       struct vduse_iova_domain *domain;
> +       struct vduse_umem *umem;
> +       struct mutex mem_lock;
> +};
> +
>  struct vduse_vq_group {
> +       rwlock_t as_lock;
> +       struct vduse_as *as; /* Protected by as_lock */
>         struct vduse_dev *dev;
>  };
>
> @@ -94,7 +104,7 @@ struct vduse_dev {
>         struct vduse_vdpa *vdev;
>         struct device *dev;
>         struct vduse_virtqueue **vqs;
> -       struct vduse_iova_domain *domain;
> +       struct vduse_as *as;
>         char *name;
>         struct mutex lock;
>         spinlock_t msg_lock;
> @@ -122,9 +132,8 @@ struct vduse_dev {
>         u32 vq_num;
>         u32 vq_align;
>         u32 ngroups;
> -       struct vduse_umem *umem;
> +       u32 nas;
>         struct vduse_vq_group *groups;
> -       struct mutex mem_lock;
>         unsigned int bounce_size;
>         struct mutex domain_lock;
>  };
> @@ -314,7 +323,7 @@ static int vduse_dev_set_status(struct vduse_dev *dev, u8 status)
>         return vduse_dev_msg_sync(dev, &msg);
>  }
>
> -static int vduse_dev_update_iotlb(struct vduse_dev *dev,
> +static int vduse_dev_update_iotlb(struct vduse_dev *dev, u32 asid,
>                                   u64 start, u64 last)
>  {
>         struct vduse_dev_msg msg = { 0 };
> @@ -323,8 +332,14 @@ static int vduse_dev_update_iotlb(struct vduse_dev *dev,
>                 return -EINVAL;
>
>         msg.req.type = VDUSE_UPDATE_IOTLB;
> -       msg.req.iova.start = start;
> -       msg.req.iova.last = last;
> +       if (dev->api_version < VDUSE_API_VERSION_1) {
> +               msg.req.iova.start = start;
> +               msg.req.iova.last = last;
> +       } else {
> +               msg.req.iova_v2.start = start;
> +               msg.req.iova_v2.last = last;
> +               msg.req.iova_v2.asid = asid;
> +       }
>
>         return vduse_dev_msg_sync(dev, &msg);
>  }
> @@ -439,11 +454,14 @@ static __poll_t vduse_dev_poll(struct file *file, poll_table *wait)
>  static void vduse_dev_reset(struct vduse_dev *dev)
>  {
>         int i;
> -       struct vduse_iova_domain *domain = dev->domain;
>
>         /* The coherent mappings are handled in vduse_dev_free_coherent() */
> -       if (domain && domain->bounce_map)
> -               vduse_domain_reset_bounce_map(domain);
> +       for (i = 0; i < dev->nas; i++) {
> +               struct vduse_iova_domain *domain = dev->as[i].domain;
> +
> +               if (domain && domain->bounce_map)
> +                       vduse_domain_reset_bounce_map(domain);
> +       }
>
>         down_write(&dev->rwsem);
>
> @@ -622,6 +640,42 @@ static union virtio_map vduse_get_vq_map(struct vdpa_device *vdpa, u16 idx)
>         return ret;
>  }
>
> +DEFINE_GUARD(vq_group_as_read_lock, struct vduse_vq_group *,
> +       if (_T->dev->nas > 1)
> +               read_lock(&_T->as_lock),
> +       if (_T->dev->nas > 1)
> +               read_unlock(&_T->as_lock))
> +
> +DEFINE_GUARD(vq_group_as_write_lock, struct vduse_vq_group *,
> +       if (_T->dev->nas > 1)
> +               write_lock(&_T->as_lock),
> +       if (_T->dev->nas > 1)
> +               write_unlock(&_T->as_lock))
> +
> +static int vduse_set_group_asid(struct vdpa_device *vdpa, unsigned int group,
> +                               unsigned int asid)
> +{
> +       struct vduse_dev *dev = vdpa_to_vduse(vdpa);
> +       struct vduse_dev_msg msg = { 0 };
> +       int r;
> +
> +       if (dev->api_version < VDUSE_API_VERSION_1)
> +               return -EINVAL;
> +
> +       msg.req.type = VDUSE_SET_VQ_GROUP_ASID;
> +       msg.req.vq_group_asid.group = group;
> +       msg.req.vq_group_asid.asid = asid;
> +
> +       r = vduse_dev_msg_sync(dev, &msg);
> +       if (r < 0)
> +               return r;
> +
> +       guard(vq_group_as_write_lock)(&dev->groups[group]);
> +       dev->groups[group].as = &dev->as[asid];
> +
> +       return 0;
> +}
> +
>  static int vduse_vdpa_get_vq_state(struct vdpa_device *vdpa, u16 idx,
>                                 struct vdpa_vq_state *state)
>  {
> @@ -793,13 +847,13 @@ static int vduse_vdpa_set_map(struct vdpa_device *vdpa,
>         struct vduse_dev *dev = vdpa_to_vduse(vdpa);
>         int ret;
>
> -       ret = vduse_domain_set_map(dev->domain, iotlb);
> +       ret = vduse_domain_set_map(dev->as[asid].domain, iotlb);
>         if (ret)
>                 return ret;
>
> -       ret = vduse_dev_update_iotlb(dev, 0ULL, ULLONG_MAX);
> +       ret = vduse_dev_update_iotlb(dev, asid, 0ULL, ULLONG_MAX);
>         if (ret) {
> -               vduse_domain_clear_map(dev->domain, iotlb);
> +               vduse_domain_clear_map(dev->as[asid].domain, iotlb);
>                 return ret;
>         }
>
> @@ -842,6 +896,7 @@ static const struct vdpa_config_ops vduse_vdpa_config_ops = {
>         .get_vq_affinity        = vduse_vdpa_get_vq_affinity,
>         .reset                  = vduse_vdpa_reset,
>         .set_map                = vduse_vdpa_set_map,
> +       .set_group_asid         = vduse_set_group_asid,
>         .get_vq_map             = vduse_get_vq_map,
>         .free                   = vduse_vdpa_free,
>  };
> @@ -850,15 +905,13 @@ static void vduse_dev_sync_single_for_device(union virtio_map token,
>                                              dma_addr_t dma_addr, size_t size,
>                                              enum dma_data_direction dir)
>  {
> -       struct vduse_dev *vdev;
>         struct vduse_iova_domain *domain;
>
>         if (!token.group)
>                 return;
>
> -       vdev = token.group->dev;
> -       domain = vdev->domain;
> -
> +       guard(vq_group_as_read_lock)(token.group);
> +       domain = token.group->as->domain;
>         vduse_domain_sync_single_for_device(domain, dma_addr, size, dir);
>  }
>
> @@ -866,15 +919,13 @@ static void vduse_dev_sync_single_for_cpu(union virtio_map token,
>                                              dma_addr_t dma_addr, size_t size,
>                                              enum dma_data_direction dir)
>  {
> -       struct vduse_dev *vdev;
>         struct vduse_iova_domain *domain;
>
>         if (!token.group)
>                 return;
>
> -       vdev = token.group->dev;
> -       domain = vdev->domain;
> -
> +       guard(vq_group_as_read_lock)(token.group);
> +       domain = token.group->as->domain;
>         vduse_domain_sync_single_for_cpu(domain, dma_addr, size, dir);
>  }
>
> @@ -883,15 +934,13 @@ static dma_addr_t vduse_dev_map_page(union virtio_map token, struct page *page,
>                                      enum dma_data_direction dir,
>                                      unsigned long attrs)
>  {
> -       struct vduse_dev *vdev;
>         struct vduse_iova_domain *domain;
>
>         if (!token.group)
>                 return DMA_MAPPING_ERROR;
>
> -       vdev = token.group->dev;
> -       domain = vdev->domain;
> -
> +       guard(vq_group_as_read_lock)(token.group);
> +       domain = token.group->as->domain;
>         return vduse_domain_map_page(domain, page, offset, size, dir, attrs);
>  }
>
> @@ -899,23 +948,19 @@ static void vduse_dev_unmap_page(union virtio_map token, dma_addr_t dma_addr,
>                                  size_t size, enum dma_data_direction dir,
>                                  unsigned long attrs)
>  {
> -       struct vduse_dev *vdev;
>         struct vduse_iova_domain *domain;
>
>         if (!token.group)
>                 return;
>
> -       vdev = token.group->dev;
> -       domain = vdev->domain;
> -
> -       return vduse_domain_unmap_page(domain, dma_addr, size, dir, attrs);
> +       guard(vq_group_as_read_lock)(token.group);
> +       domain = token.group->as->domain;
> +       vduse_domain_unmap_page(domain, dma_addr, size, dir, attrs);
>  }
>
>  static void *vduse_dev_alloc_coherent(union virtio_map token, size_t size,
>                                       dma_addr_t *dma_addr, gfp_t flag)
>  {
> -       struct vduse_dev *vdev;
> -       struct vduse_iova_domain *domain;
>         void *addr;
>
>         *dma_addr = DMA_MAPPING_ERROR;
> @@ -926,11 +971,15 @@ static void *vduse_dev_alloc_coherent(union virtio_map token, size_t size,
>         if (!addr)
>                 return NULL;
>
> -       vdev = token.group->dev;
> -       domain = vdev->domain;
> -       *dma_addr = vduse_domain_alloc_coherent(domain, size, addr);
> -       if (*dma_addr == DMA_MAPPING_ERROR)
> -               goto err;
> +       {
> +               struct vduse_iova_domain *domain;
> +
> +               guard(vq_group_as_read_lock)(token.group);
> +               domain = token.group->as->domain;
> +               *dma_addr = vduse_domain_alloc_coherent(domain, size, addr);
> +               if (*dma_addr == DMA_MAPPING_ERROR)
> +                       goto err;
> +       }

Nit: Having a standalone block probably means we have the chance to
optimize the code, maybe using a helper?

Thanks

Powered by blists - more mailing lists