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

Baolu Lu
2022-08-31T01:55:27Z

On 8/30/22 9:29 PM, Jason Gunthorpe wrote:
> On Tue, Aug 30, 2022 at 09:46:01AM +0800, Baolu Lu wrote:
>> 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.
>
> I don't think that works in the general case, you can't just destroy
> what is in group->blocking_domain..

If I understand you correctly, we can't just free the blocking domain
and forget about whether this domain is still set on any device?

>
> Maybe all of this is just the good reason to go to a simple
> device->ops->remove_dev_pasid() callback and forget about blocking
> domain here.

Do you mean rolling back to what we did in v10?

--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -262,6 +262,8 @@ struct iommu_ops {
* struct iommu_domain_ops - domain specific operations
* @attach_dev: attach an iommu domain to a device
* @detach_dev: detach an iommu domain from a device
+ * @set_dev_pasid: set an iommu domain to a pasid of device
+ * @block_dev_pasid: block pasid of device from using iommu domain
* @map: map a physically contiguous memory region to an iommu domain
* @map_pages: map a physically contiguous set of pages of the same
size to
* an iommu domain.
@@ -282,6 +284,10 @@ struct iommu_ops {
struct iommu_domain_ops {
int (*attach_dev)(struct iommu_domain *domain, struct device *dev);
void (*detach_dev)(struct iommu_domain *domain, struct device
*dev);
+ int (*set_dev_pasid)(struct iommu_domain *domain, struct device
*dev,
+ ioasid_t pasid);
+ void (*block_dev_pasid)(struct iommu_domain *domain, struct
device *dev,
+ ioasid_t pasid);

Best regards,
baolu