Messages in this thread Patch in this message | | | 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 12:28:00 +0800 |
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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); }
> Thanks, > Jean > > [1] https://lore.kernel.org/linux-iommu/20220421052121.3464100-9-baolu.lu@linux.intel.com/
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