Messages in this thread | | | Subject | Re: [PATCH v4 05/11] iommu/sva: Assign a PASID to mm on PASID allocation and free it on mm exit | From | Zhangfei Gao <> | Date | Tue, 26 Apr 2022 13:19:06 +0800 |
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On 2022/4/26 下午12:36, Fenghua Yu wrote: > On Tue, Apr 26, 2022 at 12:28:00PM +0800, Zhangfei Gao wrote: >> Hi, Jean >> >> On 2022/4/26 上午12:13, Jean-Philippe Brucker wrote: >>> Hi Jacob, >>> >>> On Mon, Apr 25, 2022 at 08:34:44AM -0700, Jacob Pan wrote: >>>> Hi Jean-Philippe, >>>> >>>> On Mon, 25 Apr 2022 15:26:40 +0100, Jean-Philippe Brucker >>>> <jean-philippe@linaro.org> wrote: >>>> >>>>> On Mon, Apr 25, 2022 at 07:18:36AM -0700, Dave Hansen wrote: >>>>>> On 4/25/22 06:53, Jean-Philippe Brucker wrote: >>>>>>> On Sat, Apr 23, 2022 at 07:13:39PM +0800, zhangfei.gao@foxmail.com >>>>>>> wrote: >>>>>>>>>> On 5.17 >>>>>>>>>> fops_release is called automatically, as well as >>>>>>>>>> iommu_sva_unbind_device. On 5.18-rc1. >>>>>>>>>> fops_release is not called, have to manually call close(fd) >>>>>>>>> Right that's weird >>>>>>>> Looks it is caused by the fix patch, via mmget, which may add >>>>>>>> refcount of fd. >>>>>>> Yes indirectly I think: when the process mmaps the queue, >>>>>>> mmap_region() takes a reference to the uacce fd. That reference is >>>>>>> released either by explicit close() or munmap(), or by exit_mmap() >>>>>>> (which is triggered by mmput()). Since there is an mm->fd dependency, >>>>>>> we cannot add a fd->mm dependency, so no mmget()/mmput() in >>>>>>> bind()/unbind(). >>>>>>> >>>>>>> I guess we should go back to refcounted PASIDs instead, to avoid >>>>>>> freeing them until unbind(). >>>>>> Yeah, this is a bit gnarly for -rc4. Let's just make sure there's >>>>>> nothing else simple we can do. >>>>>> >>>>>> How does the IOMMU hardware know that all activity to a given PASID is >>>>>> finished? That activity should, today, be independent of an mm or a >>>>>> fd's lifetime. >>>>> In the case of uacce, it's tied to the fd lifetime: opening an accelerator >>>>> queue calls iommu_sva_bind_device(), which sets up the PASID context in >>>>> the IOMMU. Closing the queue calls iommu_sva_unbind_device() which >>>>> destroys the PASID context (after the device driver stopped all DMA for >>>>> this PASID). >>>>> >>>> For VT-d, it is essentially the same flow except managed by the individual >>>> drivers such as DSA. >>>> If free() happens before unbind(), we deactivate the PASIDs and suppress >>>> faults from the device. When the unbind finally comes, we finalize the >>>> PASID teardown. It seems we have a need for an intermediate state where >>>> PASID is "pending free"? >>> Yes we do have that state, though I'm not sure we need to make it explicit >>> in the ioasid allocator. >>> >>> Could we move mm_pasid_drop() to __mmdrop() instead of __mmput()? For Arm >>> we do need to hold the mm_count until unbind(), and mmgrab()/mmdrop() is >>> also part of Lu's rework [1]. >> Move mm_pasid_drop to __mmdrop looks workable. >> >> The nginx works since ioasid is not freed when master exit until nginx stop. >> >> The ioasid does not free immediately when fops_release->unbind finished. >> Instead, __mmdrop happens a bit lazy, which has no issue though >> I passed 10000 times exit without unbind test, the pasid allocation is ok. >> >> Thanks >> >> >> diff --git a/kernel/fork.c b/kernel/fork.c >> index 9796897560ab..60f417f69367 100644 >> --- a/kernel/fork.c >> +++ b/kernel/fork.c >> @@ -792,6 +792,8 @@ void __mmdrop(struct mm_struct *mm) >> mmu_notifier_subscriptions_destroy(mm); >> check_mm(mm); >> put_user_ns(mm->user_ns); >> + mm_pasid_drop(mm); >> free_mm(mm); >> } >> EXPORT_SYMBOL_GPL(__mmdrop); >> @@ -1190,7 +1192,6 @@ static inline void __mmput(struct mm_struct *mm) >> } >> if (mm->binfmt) >> module_put(mm->binfmt->module); >> - mm_pasid_drop(mm); >> mmdrop(mm); >> } > Thank you very much, Zhangfei! > > I just now sent out an identical patch. It works on X86 as well. > > So seems the patch is the right fix. > > Either you can send out the patch or I add your Signed-off-by? Either way > is OK for me. Thanks Fenghua, It does not matter. Have added tested-by. I was in stress test for checking the pasid free, since it was freed lazily.
Thank all for the help, a bit nervous, since it is rc4 now.
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