On Tue, May 16, 2023 at 11:00:16AM +0800, Baolu Lu wrote:
> On 5/15/23 10:00 PM, Jason Gunthorpe wrote:
> > The devices list was used as a simple way to avoid having per-group
> > information. Now that this seems to be unavoidable, just commit to
> > per-group information fully and remove the devices list from the HWPT.
> >
> > The iommufd_group stores the currently assigned HWPT for the entire group
> > and we can manage the per-device attach/detach with a list in the
> > iommufd_group.
>
> I am preparing the patches to route I/O page faults to user space
> through iommufd. The iommufd page fault handler knows the hwpt and the
> device pointer, but it needs to convert the device pointer into its
> iommufd object id and pass the id to user space.
>
> It's fine that we remove the hwpt->devices here, but perhaps I need to
> add the context pointer in ioas later,
>
> struct iommufd_ioas {
> struct io_pagetable iopt;
> struct mutex mutex;
> struct list_head hwpt_list;
> + struct iommufd_ctx *ictx;
> };
>
> and, use below helper to look up the device id.
>
> +u32 iommufd_get_device_id(struct iommufd_ctx *ictx, struct device *dev)
> +{
> + struct iommu_group *group = iommu_group_get(dev);
> + u32 dev_id = IOMMUFD_INVALID_OBJ_ID;
> + struct iommufd_group *igroup;
> + struct iommufd_device *cur;
> + unsigned int id;
> +
> + if (!group)
> + return IOMMUFD_INVALID_OBJ_ID;
> +
> + id = iommu_group_id(group);
> + xa_lock(&ictx->groups);
> + igroup = xa_load(&ictx->groups, id);
> + if (!iommufd_group_try_get(igroup, group)) {
> + xa_unlock(&ictx->groups);
> + iommu_group_put(group);
> + return IOMMUFD_INVALID_OBJ_ID;
> + }
> + xa_unlock(&ictx->groups);
> +
> + mutex_lock(&igroup->lock);
> + list_for_each_entry(cur, &igroup->device_list, group_item) {
> + if (cur->dev == dev) {
> + dev_id = cur->obj.id;
> + break;
> + }
> + }
I dislike how slow this is on something resembling a fastish path :\
Maybe we should stash something in the dev_iommu instead?
Or can the PRI stuff provide a cookie per-device?
But it will work like this
> dev_id = iommufd_get_device_id(hwpt->ioas->ictx, dev);
Where did the hwpt come from?
Jason
