Re: [PATCH v5 1/9] iommu: Introduce domain attachment handle

[Baolu Lu]

On 5/15/24 3:17 PM, Tian, Kevin wrote:
> > From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Tuesday, April 30, 2024 10:57 PM
> >
> > +/* Add an attach handle to the group's pasid array. */
> > +static struct iommu_attach_handle *
> > +iommu_attach_handle_set(struct iommu_domain *domain,
> > +			struct iommu_group *group, ioasid_t pasid)
> > +{
> > +	struct iommu_attach_handle *handle;
> > +	void *curr;
> > +
> > +	handle = kzalloc(sizeof(*handle), GFP_KERNEL);
> > +	if (!handle)
> > +		return ERR_PTR(-ENOMEM);
> > +
> > +	handle->domain = domain;
> > +	curr = xa_cmpxchg(&group->pasid_array, pasid, NULL, handle,
> > GFP_KERNEL);
>
> this could be just xa_insert() which returns -EBUSY if the entry isn't NULL.

Yes, exactly.

> > +	if (curr) {
> > +		kfree(handle);
> > +		return xa_err(curr) ? curr : ERR_PTR(-EBUSY);
>
> 'curr' is not an error pointer. You need ERR_PTR(xa_err(curr)).

Fixed.

> >   int iommu_attach_group(struct iommu_domain *domain, struct
> > iommu_group *group)
> >   {
> > +	struct iommu_attach_handle *handle;
> >   	int ret;
> >
> >   	mutex_lock(&group->mutex);
> > +	handle = iommu_attach_handle_set(domain, group,
> > IOMMU_NO_PASID);
> > +	if (IS_ERR(handle)) {
> > +		ret = PTR_ERR(handle);
> > +		goto out_unlock;
> > +	}
> >   	ret = __iommu_attach_group(domain, group);
> > +	if (ret)
> > +		goto out_remove_handle;
> >   	mutex_unlock(&group->mutex);
>
> It's slightly better to set the handler after __iommu_attach_group().
>
> doing so is aligned to the sequence in iommu_group_replace_domain().

I did it in this way because erasing an attach handle is easier than
rolling back the group to the previous domain from the perspective of
coding. I didn't realize attaching the group and storing the attach
handle had to be done in a specific order.

> > @@ -2211,13 +2307,33 @@ EXPORT_SYMBOL_GPL(iommu_attach_group);
> >   int iommu_group_replace_domain(struct iommu_group *group,
> >   			       struct iommu_domain *new_domain)
> >   {
> > +	struct iommu_domain *old_domain = group->domain;
> > +	struct iommu_attach_handle *handle;
> >   	int ret;
> >
> >   	if (!new_domain)
> >   		return -EINVAL;
> >
> > +	if (new_domain == old_domain)
> > +		return 0;
> > +
>
> __iommu_group_set_domain() already does the check.

Removed.

Best regards,
baolu