On Thu, Feb 10, 2022 at 08:27:50AM -0800, Fenghua Yu wrote: > Hi, Jacob, > > On Wed, Feb 09, 2022 at 07:16:14PM -0800, Jacob Pan wrote: > > Hi Fenghua, > > > > On Mon, 7 Feb 2022 15:02:48 -0800, Fenghua Yu <fenghua...@intel.com> wrote: > > > > > @@ -1047,8 +1040,6 @@ struct iommu_sva *intel_svm_bind(struct device > > > *dev, struct mm_struct *mm, void } > > > > > > sva = intel_svm_bind_mm(iommu, dev, mm, flags); > > > - if (IS_ERR_OR_NULL(sva)) > > > - intel_svm_free_pasid(mm); > > If bind fails, the PASID has no IOMMU nor CPU context. It should be safe to > > free here. > > The PASID can not be freed even if bind fails. The PASID allocated earlier > (either in this thread or in another thread) might be populated to other > threads already and being used now. > > Without freeing the PASID on bind failure, the worst case is the PASID might > not be used in the process (and will be freed on process exit anyway). > > This all matches with the PASID life time described in the commit message.
But what does this mean for the user that failed that intel_svm_bind_mm()? Here's a scenario: Process sets up to use PASID capable device #1. Everything works, so the process has mm->pasid, and the IOMMU has the tables to map virtual addresses coming from device #1 using that PASID. Now the same process asks to start using PASID capable device #2, but there is a failure at intel_svm_bind_mm(). Fenghua is right that we shouldn't free the PASID. It is in use by at least one thread of the process to access device #1. But what happens with device #2? Does the caller of intel_svm_bind() do the right thing with the IS_ERR_OR_NULL return value to let the user know that device #2 isn't accessible? -Tony _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
