Re: [PATCH v7 04/10] iommu: Extend domain attach group with handle support

[Jason Gunthorpe]

On Sun, Jun 16, 2024 at 02:11:49PM +0800, Lu Baolu wrote:

> +int iommu_replace_group_handle(struct iommu_group *group,
> +                            struct iommu_domain *new_domain,
> +                            struct iommu_attach_handle *handle)
> +{
> +     struct iommu_domain *old_domain = group->domain;
> +     void *curr;
> +     int ret;
> +
> +     if (!new_domain)
> +             return -EINVAL;
> +
> +     mutex_lock(&group->mutex);
> +     ret = __iommu_group_set_domain(group, new_domain);
> +     if (ret)
> +             goto err_unlock;
> +     xa_erase(&group->pasid_array, IOMMU_NO_PASID);
> +     if (handle) {
> +             curr = xa_store(&group->pasid_array, IOMMU_NO_PASID, handle, 
> GFP_KERNEL);
> +             if (xa_err(curr)) {
> +                     ret = xa_err(curr);
> +                     goto err_restore;

But this error unwind doesn't work because the xa_erase() already
happened and there may have been a handle there that we don't put
back.

Something like this - store to a reserved entry cannot fail:

int iommu_replace_group_handle(struct iommu_group *group,
                               struct iommu_domain *new_domain,
                               struct iommu_attach_handle *handle)
{
        void *curr;
        int ret;

        if (!new_domain)
                return -EINVAL;

        mutex_lock(&group->mutex);
        if (handle) {
                ret = xa_reserve(&group->pasid_array, IOMMU_NO_PASID,
                                 GFP_KERNEL);
                if (ret)
                        goto err_unlock;
        }

        ret = __iommu_group_set_domain(group, new_domain);
        if (ret)
                goto err_release;

        curr = xa_store(&group->pasid_array, IOMMU_NO_PASID, handle,
                        GFP_KERNEL);
        WARN_ON(xa_is_err(curr));

        mutex_unlock(&group->mutex);

        return 0;
err_release:
        xa_release(&group->pasid_array, IOMMU_NO_PASID);
err_unlock:
        mutex_unlock(&group->mutex);
        return ret;
}

Jason