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

Baolu Lu
2022-08-30T01:46:19Z

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@linux.intel.com>
>>>> Tested-by: Zhangfei Gao<zhangfei.gao@linaro.org>
>>>> Tested-by: Tony Zhu<tony.zhu@intel.com>
>>>> ---
>>>> 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