On Fri, Apr 29, 2022 at 06:51:17AM -0700, Fenghua Yu wrote: > Hi, Baolu, > > On Fri, Apr 29, 2022 at 03:53:57PM +0800, Baolu Lu wrote: > > On 2022/4/28 16:39, Jean-Philippe Brucker wrote: > > > > The address space is what the OOM killer is after. That gets refcounted > > > > with mmget()/mmput()/mm->mm_users. The OOM killer is satiated by the > > > > page freeing done in __mmput()->exit_mmap(). > > > > > > > > Also, all the VMAs should be gone after exit_mmap(). So, even if > > > > vma->vm_file was holding a reference to a device driver, that reference > > > > should be gone by the time __mmdrop() is actually freeing the PASID. > > > > > > I agree with all that. The concern was about tearing down the PASID in the > > > IOMMU and device from the release() MMU notifier, which would happen in > > > exit_mmap(). But doing the teardown at or before __mmdrop() is fine. And > > > since the IOMMU drivers need to hold mm->mm_count anyway between bind() > > > and unbind(), I think Fenghua's fix works. > > > > But I didn't find mmgrab()/mmdrop() get called in both arm and intel > > IOMMU drivers. > > > > $ git grep mmgrab drivers/iommu/ > > [no output] > > > > Do we need to add these in a separated fix patch, or I missed anything > > here? > > On both ARM and X86, sva_bind() calls mmu_notifier_register()->mmgrab() and > sva_unbind() calls mmu_notifier_unregister()/mmu_notifier_put()->mmdrop().
Yes, although for Arm I realized the mmu_notifier grab wasn't sufficient so I sent a separate fix that should go in 5.18 as well https://lore.kernel.org/linux-iommu/[email protected]/ The Arm driver still touches the arch mm context after mmu_notifier_put(). I don't think X86 has that problem. Thanks, Jean > So mm->mm_count are already counted in existing ARM and X86 binding and > unbinding. The fix patch just frees the PASID in __mmdrop() after > no more mm->mm_count. > > There is no need to add extra mmgrab() and mmdrop() pair. > > Thanks. > > -Fenghua > > _______________________________________________ iommu mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/iommu
