Re: [PATCH v12 07/17] iommu: Try to allocate blocking domain when probing device

[Baolu Lu]

On 2022/8/30 01:27, Jason Gunthorpe wrote:
> On Mon, Aug 29, 2022 at 11:40:24AM +0800, Baolu Lu wrote:
> > On 2022/8/26 22:52, Jason Gunthorpe wrote:
> > > On Fri, Aug 26, 2022 at 08:11:31PM +0800, Lu Baolu wrote:
> > > > Allocate the blocking domain when probing devices if the driver supports
> > > > blocking domain allocation. Otherwise, revert to the previous behavior,
> > > > that is, use UNMANAGED domain instead when the blocking domain is needed.
> > > >
> > > > Signed-off-by: Lu Baolu<baolu.lu@xxxxxxxxxxxxxxx>
> > > > Tested-by: Zhangfei Gao<zhangfei.gao@xxxxxxxxxx>
> > > > Tested-by: Tony Zhu<tony.zhu@xxxxxxxxx>
> > > > ---
> > > >    drivers/iommu/iommu.c | 29 +++++++++++++++++------------
> > > >    1 file changed, 17 insertions(+), 12 deletions(-)
> > > This seems like a lot of overhead to allocate these things for every
> > > group?
> > >
> > > Why not add a simple refcount on the blocking domain instead and
> > > allocate the domain on the pasid attach like we do for ownership?
> >
> > I am working towards implementing static instance of blocking domain for
> > each IOMMU driver, and then, there's no much overhead to allocate it in
> > the probing device path.
>
> Well, I thought about that and I don't think we can get
> there in a short order.

Yes. Fair enough.

> Would rather you progress this series without
> getting entangled in such a big adventure

Agreed. I will drop this patch and add below code in the iommu
interface:

--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -3219,6 +3219,26 @@ int iommu_attach_device_pasid(struct iommu_domain 
*domain,
                return -ENODEV;

        mutex_lock(&group->mutex);
+
+       /*
+        * The underlying IOMMU driver needs to support blocking domain
+        * allocation and the callback to block DMA transactions with a
+        * specific PASID.
+        */
+       if (!group->blocking_domain) {
+               group->blocking_domain = __iommu_domain_alloc(dev->bus,
+                               IOMMU_DOMAIN_BLOCKED);
+               if (!group->blocking_domain) {
+                       ret = -ENODEV;
+                       goto out_unlock;
+               }
+       }
+
+       if (!group->blocking_domain->ops->set_dev_pasid) {
+               ret = -EOPNOTSUPP;
+               goto out_unlock;
+       }
+
        curr = xa_cmpxchg(&group->pasid_array, pasid, NULL, domain, 
GFP_KERNEL);
        if (curr) {
                ret = xa_err(curr) ? : -EBUSY;

Currently both ARM SMMUv3 and VT-d drivers use static blocking domain.
Hence I didn't use a refcount for blocking domain release here.

Best regards,
baolu