RE: [RFC PATCH v2 10/19] vhost-vdpa: introduce asid based IOTLB

[Gautam Dawar]

-----Original Message-----
From: Eugenio Perez Martin <eperezma@xxxxxxxxxx> 
Sent: Friday, March 4, 2022 11:26 PM
To: Gautam Dawar <gdawar@xxxxxxxxxx>
Cc: Gautam Dawar <gdawar@xxxxxxxxxx>; Martin Petrus Hubertus Habets <martinh@xxxxxxxxxx>; Harpreet Singh Anand <hanand@xxxxxxxxxx>; Tanuj Murlidhar Kamde <tanujk@xxxxxxxxxx>; Jason Wang <jasowang@xxxxxxxxxx>; Michael S. Tsirkin <mst@xxxxxxxxxx>; Zhu Lingshan <lingshan.zhu@xxxxxxxxx>; Stefano Garzarella <sgarzare@xxxxxxxxxx>; Xie Yongji <xieyongji@xxxxxxxxxxxxx>; Eli Cohen <elic@xxxxxxxxxx>; Si-Wei Liu <si-wei.liu@xxxxxxxxxx>; Parav Pandit <parav@xxxxxxxxxx>; Longpeng <longpeng2@xxxxxxxxxx>; virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; kvm list <kvm@xxxxxxxxxxxxxxx>; netdev@xxxxxxxxxxxxxxx
Subject: Re: [RFC PATCH v2 10/19] vhost-vdpa: introduce asid based IOTLB

On Thu, Feb 24, 2022 at 10:26 PM Gautam Dawar <gautam.dawar@xxxxxxxxxx> wrote:
>
> This patch converts the vhost-vDPA device to support multiple IOTLBs 
> tagged via ASID via hlist. This will be used for supporting multiple 
> address spaces in the following patches.
>
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> Signed-off-by: Gautam Dawar <gdawar@xxxxxxxxxx>
> ---
>  drivers/vhost/vdpa.c | 104 
> ++++++++++++++++++++++++++++++++-----------
>  1 file changed, 79 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c index 
> d0aacc0cc79a..4e8b7c4809cd 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -33,13 +33,21 @@ enum {
>
>  #define VHOST_VDPA_DEV_MAX (1U << MINORBITS)
>
> +#define VHOST_VDPA_IOTLB_BUCKETS 16
> +
> +struct vhost_vdpa_as {
> +       struct hlist_node hash_link;
> +       struct vhost_iotlb iotlb;
> +       u32 id;
> +};
> +
>  struct vhost_vdpa {
>         struct vhost_dev vdev;
>         struct iommu_domain *domain;
>         struct vhost_virtqueue *vqs;
>         struct completion completion;
>         struct vdpa_device *vdpa;
> -       struct vhost_iotlb *iotlb;
> +       struct hlist_head as[VHOST_VDPA_IOTLB_BUCKETS];
>         struct device dev;
>         struct cdev cdev;
>         atomic_t opened;
> @@ -49,12 +57,64 @@ struct vhost_vdpa {
>         struct eventfd_ctx *config_ctx;
>         int in_batch;
>         struct vdpa_iova_range range;
> +       int used_as;

This member is only modified to count the number of AS, but is never read again. In patch 15/19 is deleted. Could we avoid introducing it in all the series?

This is also in the previous series, but it was declared useless if I recall correctly.
[GD>>] Yes, it makes sense to remove used_as structure member. Will do.

>  };
>
>  static DEFINE_IDA(vhost_vdpa_ida);
>
>  static dev_t vhost_vdpa_major;
>
> +static struct vhost_vdpa_as *asid_to_as(struct vhost_vdpa *v, u32 
> +asid) {
> +       struct hlist_head *head = &v->as[asid % VHOST_VDPA_IOTLB_BUCKETS];
> +       struct vhost_vdpa_as *as;
> +
> +       hlist_for_each_entry(as, head, hash_link)
> +               if (as->id == asid)
> +                       return as;
> +
> +       return NULL;
> +}
> +
> +static struct vhost_vdpa_as *vhost_vdpa_alloc_as(struct vhost_vdpa 
> +*v, u32 asid) {
> +       struct hlist_head *head = &v->as[asid % VHOST_VDPA_IOTLB_BUCKETS];
> +       struct vhost_vdpa_as *as;
> +
> +       if (asid_to_as(v, asid))
> +               return NULL;
> +
> +       as = kmalloc(sizeof(*as), GFP_KERNEL);
> +       if (!as)
> +               return NULL;
> +
> +       vhost_iotlb_init(&as->iotlb, 0, 0);
> +       as->id = asid;
> +       hlist_add_head(&as->hash_link, head);
> +       ++v->used_as;
> +
> +       return as;
> +}
> +
> +static int vhost_vdpa_remove_as(struct vhost_vdpa *v, u32 asid) {
> +       struct vhost_vdpa_as *as = asid_to_as(v, asid);
> +
> +       /* Remove default address space is not allowed */
> +       if (asid == 0)
> +               return -EINVAL;

We must remove address space id 0 so we don't leak it at vhost_vdpa_cleanup. I think the check could go away with no need of moving it.
[GD>>] Good catch. Will remove this check to allow freeing "as" for asid 0 in vhost_vdpa_cleanup()

> +
> +       if (!as)
> +               return -EINVAL;
> +
> +       hlist_del(&as->hash_link);
> +       vhost_iotlb_reset(&as->iotlb);
> +       kfree(as);
> +       --v->used_as;
> +
> +       return 0;
> +}
> +
>  static void handle_vq_kick(struct vhost_work *work)  {
>         struct vhost_virtqueue *vq = container_of(work, struct 
> vhost_virtqueue, @@ -554,15 +614,6 @@ static void vhost_vdpa_iotlb_unmap(struct vhost_vdpa *v,
>         return vhost_vdpa_pa_unmap(v, iotlb, start, last);  }
>
> -static void vhost_vdpa_iotlb_free(struct vhost_vdpa *v) -{
> -       struct vhost_iotlb *iotlb = v->iotlb;
> -
> -       vhost_vdpa_iotlb_unmap(v, iotlb, 0ULL, 0ULL - 1);
> -       kfree(v->iotlb);
> -       v->iotlb = NULL;
> -}
> -
>  static int perm_to_iommu_flags(u32 perm)  {
>         int flags = 0;
> @@ -842,7 +893,8 @@ static int vhost_vdpa_process_iotlb_msg(struct vhost_dev *dev, u32 asid,
>         struct vhost_vdpa *v = container_of(dev, struct vhost_vdpa, vdev);
>         struct vdpa_device *vdpa = v->vdpa;
>         const struct vdpa_config_ops *ops = vdpa->config;
> -       struct vhost_iotlb *iotlb = v->iotlb;
> +       struct vhost_vdpa_as *as = asid_to_as(v, 0);
> +       struct vhost_iotlb *iotlb = &as->iotlb;
>         int r = 0;
>
>         mutex_lock(&dev->mutex);
> @@ -953,6 +1005,13 @@ static void vhost_vdpa_set_iova_range(struct vhost_vdpa *v)
>         }
>  }
>
> +static void vhost_vdpa_cleanup(struct vhost_vdpa *v) {
> +       vhost_dev_cleanup(&v->vdev);
> +       kfree(v->vdev.vqs);
> +       vhost_vdpa_remove_as(v, 0);
> +}
> +
>  static int vhost_vdpa_open(struct inode *inode, struct file *filep)  
> {
>         struct vhost_vdpa *v;
> @@ -985,15 +1044,12 @@ static int vhost_vdpa_open(struct inode *inode, struct file *filep)
>         vhost_dev_init(dev, vqs, nvqs, 0, 0, 0, false,
>                        vhost_vdpa_process_iotlb_msg);
>
> -       v->iotlb = vhost_iotlb_alloc(0, 0);
> -       if (!v->iotlb) {
> -               r = -ENOMEM;
> -               goto err_init_iotlb;
> -       }
> +       if (!vhost_vdpa_alloc_as(v, 0))
> +               goto err_alloc_as;
>
>         r = vhost_vdpa_alloc_domain(v);
>         if (r)
> -               goto err_alloc_domain;
> +               goto err_alloc_as;
>
>         vhost_vdpa_set_iova_range(v);
>
> @@ -1001,11 +1057,8 @@ static int vhost_vdpa_open(struct inode *inode, 
> struct file *filep)
>
>         return 0;
>
> -err_alloc_domain:
> -       vhost_vdpa_iotlb_free(v);
> -err_init_iotlb:
> -       vhost_dev_cleanup(&v->vdev);
> -       kfree(vqs);
> +err_alloc_as:
> +       vhost_vdpa_cleanup(v);
>  err:
>         atomic_dec(&v->opened);
>         return r;
> @@ -1029,11 +1082,9 @@ static int vhost_vdpa_release(struct inode *inode, struct file *filep)
>         vhost_vdpa_clean_irq(v);
>         vhost_vdpa_reset(v);
>         vhost_dev_stop(&v->vdev);
> -       vhost_vdpa_iotlb_free(v);
>         vhost_vdpa_free_domain(v);
>         vhost_vdpa_config_put(v);
>         vhost_dev_cleanup(&v->vdev);
> -       kfree(v->vdev.vqs);
>         mutex_unlock(&d->mutex);
>
>         atomic_dec(&v->opened);
> @@ -1129,7 +1180,7 @@ static int vhost_vdpa_probe(struct vdpa_device *vdpa)
>         const struct vdpa_config_ops *ops = vdpa->config;
>         struct vhost_vdpa *v;
>         int minor;
> -       int r;
> +       int i, r;
>
>         /* Only support 1 address space and 1 groups */
>         if (vdpa->ngroups != 1 || vdpa->nas != 1) @@ -1177,6 +1228,9 
> @@ static int vhost_vdpa_probe(struct vdpa_device *vdpa)
>         init_completion(&v->completion);
>         vdpa_set_drvdata(vdpa, v);
>
> +       for (i = 0; i < VHOST_VDPA_IOTLB_BUCKETS; i++)
> +               INIT_HLIST_HEAD(&v->as[i]);
> +
>         return 0;
>
>  err:
> --
> 2.25.0
>