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Message-ID: <CACGkMEuwzmSmrh5PBhuokzt6Tf5b4+6JGmAuTAC-y-Sm04FZPA@mail.gmail.com>
Date: Fri, 14 Nov 2025 08:55:21 +0800
From: Jason Wang <jasowang@...hat.com>
To: Eugenio Pérez <eperezma@...hat.com>
Cc: "Michael S . Tsirkin" <mst@...hat.com>, Laurent Vivier <lvivier@...hat.com>, virtualization@...ts.linux.dev,
Maxime Coquelin <mcoqueli@...hat.com>, Cindy Lu <lulu@...hat.com>, linux-kernel@...r.kernel.org,
Yongji Xie <xieyongji@...edance.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
Stefano Garzarella <sgarzare@...hat.com>
Subject: Re: [PATCH v9 5/6] vduse: add vq group asid support
On Thu, Nov 13, 2025 at 7:56 PM 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.
>
> Now that the driver can change ASID in the middle of operation, the
> domain that each vq address point is also protected by domain_lock.
Maybe it's better to document what is protected by RCU and how.
More below.
>
> Acked-by: Jason Wang <jasowang@...hat.com>
> Signed-off-by: Eugenio Pérez <eperezma@...hat.com>
> ---
> v9:
> * Replace mutex with RCU, 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 | 370 ++++++++++++++++++++---------
> include/uapi/linux/vduse.h | 53 ++++-
> 2 files changed, 314 insertions(+), 109 deletions(-)
>
> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> index 97be04f73fbf..ff95ed56f22d 100644
> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> @@ -11,6 +11,7 @@
> #include "linux/virtio_net.h"
> #include <linux/init.h>
> #include <linux/module.h>
> +#include <linux/rcupdate.h>
> #include <linux/cdev.h>
> #include <linux/device.h>
> #include <linux/eventfd.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 +88,14 @@ 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 {
> + struct vduse_as *as __rcu;
> struct vduse_dev *dev;
> };
>
> @@ -94,7 +103,7 @@ 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 +131,8 @@ 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 +322,7 @@ 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 +331,14 @@ 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);
> }
> @@ -436,14 +450,32 @@ static __poll_t vduse_dev_poll(struct file *file, poll_table *wait)
> return mask;
> }
>
> +/* Force set the asid to a vq group without a message to the VDUSE device */
> +static void vduse_set_group_asid_nomsg(struct vduse_dev *dev,
> + unsigned int group, unsigned int asid)
> +{
> + /*
> + * Two concurrent updates to this pointer are valid as they cannot
> + * point to an invalid region. It is ok for them to race as long as
> + * the readers see a consistent state through RCU.
> + */
> + rcu_assign_pointer(dev->groups[group].as, &dev->as[asid]);
I'd expect at least a synchronize_rcu() here to wait for the read is done?
> +}
> +
> 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);
> + }
> +
> + for (i = 0; i < dev->ngroups; i++)
> + vduse_set_group_asid_nomsg(dev, i, 0);
>
> down_write(&dev->rwsem);
>
> @@ -623,6 +655,29 @@ static union virtio_map vduse_get_vq_map(struct vdpa_device *vdpa, u16 idx)
> return ret;
> }
>
> +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 ||
> + group >= dev->ngroups || asid >= dev->nas)
> + 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;
> +
> + vduse_set_group_asid_nomsg(dev, group, asid);
> + return 0;
> +}
> +
> static int vduse_vdpa_get_vq_state(struct vdpa_device *vdpa, u16 idx,
> struct vdpa_vq_state *state)
> {
> @@ -794,13 +849,13 @@ 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;
> }
>
> @@ -843,6 +898,7 @@ 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,
> };
> @@ -852,14 +908,17 @@ static void vduse_dev_sync_single_for_device(union virtio_map token,
> enum dma_data_direction dir)
> {
> struct vduse_dev *vdev;
> + struct vduse_as *as;
> struct vduse_iova_domain *domain;
>
> if (!token.group)
> return;
>
> vdev = token.group->dev;
> - domain = vdev->domain;
> -
> + rcu_read_lock();
> + as = rcu_dereference(token.group->as);
> + domain = as->domain;
> + rcu_read_unlock();
> vduse_domain_sync_single_for_device(domain, dma_addr, size, dir);
This is suspicious, at least we should do rcu_read_unlock() after
vduse_domain_sync_single_for_device(), otherwise I don't see how RCU
works.
> }
>
> @@ -868,14 +927,17 @@ static void vduse_dev_sync_single_for_cpu(union virtio_map token,
> enum dma_data_direction dir)
> {
> struct vduse_dev *vdev;
> + struct vduse_as *as;
> struct vduse_iova_domain *domain;
>
> if (!token.group)
> return;
>
> vdev = token.group->dev;
> - domain = vdev->domain;
> -
> + rcu_read_lock();
> + as = rcu_dereference(token.group->as);
> + domain = as->domain;
> + rcu_read_unlock();
> vduse_domain_sync_single_for_cpu(domain, dma_addr, size, dir);
> }
>
> @@ -885,15 +947,21 @@ static dma_addr_t vduse_dev_map_page(union virtio_map token, struct page *page,
> unsigned long attrs)
> {
> struct vduse_dev *vdev;
> + struct vduse_as *as;
> struct vduse_iova_domain *domain;
> + dma_addr_t r;
>
> if (!token.group)
> return DMA_MAPPING_ERROR;
>
> vdev = token.group->dev;
> - domain = vdev->domain;
> + rcu_read_lock();
> + as = rcu_dereference(token.group->as);
> + domain = as->domain;
> + rcu_read_unlock();
> + r = vduse_domain_map_page(domain, page, offset, size, dir, attrs);
Same here.
Thanks
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