Messages in this thread | | | Date | Fri, 29 Apr 2022 14:17:23 +0800 | Subject | Re: [PATCH v4 10/12] iommu: Prepare IOMMU domain for IOPF | From | Baolu Lu <> |
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Hi Jean,
On 2022/4/28 22:47, Jean-Philippe Brucker wrote: > Hi Baolu, > > On Thu, Apr 21, 2022 at 01:21:19PM +0800, Lu Baolu wrote: >> +/* >> + * Get the attached domain for asynchronous usage, for example the I/O >> + * page fault handling framework. The caller get a reference counter >> + * of the domain automatically on a successful return and should put >> + * it with iommu_domain_put() after usage. >> + */ >> +struct iommu_domain * >> +iommu_get_domain_for_dev_pasid_async(struct device *dev, ioasid_t pasid) >> +{ >> + struct iommu_domain *domain; >> + struct iommu_group *group; >> + >> + if (!pasid_valid(pasid)) >> + return NULL; >> + >> + group = iommu_group_get(dev); >> + if (!group) >> + return NULL; >> + >> + mutex_lock(&group->mutex); > > There is a possible deadlock between unbind() and the fault handler: > > unbind() iopf_handle_group() > mutex_lock(&group->mutex) > iommu_detach_device_pasid() > iopf_queue_flush_dev() iommu_get_domain_for_dev_pasid_async() > ... waits for IOPF work mutex_lock(&group->mutex) >
Yes, really.
> I was wrong in my previous review: we do have a guarantee that the SVA > domain does not go away during IOPF handling, because unbind() waits for > pending faults with iopf_queue_flush_dev() before freeing the domain (or > for Arm stall, knows that there are no pending faults). So we can just get > rid of domain->async_users and the group->mutex in IOPF, I think?
Agreed with you. The Intel code does the same thing in its unbind().
Thus, the sva domain's life cycle has already synchronized with IOPF handling, there's no need for domain->async.
I will drop it in the next version. Thanks you!
Best regards, baolu
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