Re: [bug report] iommu/arm-smmu-v3: Event cannot be printed in some scenarios

[Baolu Lu <baolu.lu@linux.intel.com>]

On 2024/8/5 23:32, Pranjal Shrivastava wrote:
> On Mon, Aug 05, 2024 at 01:30:01PM +0100, Will Deacon wrote:
>> On Mon, Aug 05, 2024 at 08:13:09PM +0800, Kunkun Jiang wrote:
>>> On 2024/8/2 22:38, Pranjal Shrivastava wrote:
>>>> Hey,
>>>> On Mon, Jul 29, 2024 at 11:02 AM Baolu Lu<baolu.lu@linux.intel.com>  wrote:
>>>>> On 2024/7/24 18:24, Will Deacon wrote:
>>>>>> On Wed, Jul 24, 2024 at 05:22:59PM +0800, Kunkun Jiang wrote:
>>>>>>> On 2024/7/24 9:42, Kunkun Jiang wrote:
>>>>>>>> drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>>>>>>>> 1797                 while (!queue_remove_raw(q, evt)) {
>>>>>>>> 1798                         u8 id = FIELD_GET(EVTQ_0_ID, evt[0]);
>>>>>>>> 1799
>>>>>>>> 1800                         ret = arm_smmu_handle_evt(smmu, evt);
>>>>>>>> 1801                         if (!ret || !__ratelimit(&rs))
>>>>>>>> 1802                                 continue;
>>>>>>>> 1803
>>>>>>>> 1804                         dev_info(smmu->dev, "event 0x%02x
>>>>>>>> received:\n", id);
>>>>>>>> 1805                         for (i = 0; i < ARRAY_SIZE(evt); ++i)
>>>>>>>> 1806                                 dev_info(smmu->dev, "\t0x%016llx\n",
>>>>>>>> 1807                                          (unsigned long
>>>>>>>> long)evt[i]);
>>>>>>>> 1808
>>>>>>>> 1809                         cond_resched();
>>>>>>>> 1810                 }
>>>>>>>>
>>>>>>>> The smmu-v3 driver cannot print event information when "ret" is 0.
>>>>>>>> Unfortunately due to commit 3dfa64aecbaf
>>>>>>>> ("iommu: Make iommu_report_device_fault() return void"), the default
>>>>>>>> return value in arm_smmu_handle_evt() is 0. Maybe a trace should
>>>>>>>> be added here?
>>>>>>> Additional explanation. Background introduction:
>>>>>>> 1.A device(VF) is passthrough(VFIO-PCI) to a VM.
>>>>>>> 2.The SMMU has the stall feature.
>>>>>>> 3.Modified guest device driver to generate an event.
>>>>>>>
>>>>>>> This event handling process is as follows:
>>>>>>> arm_smmu_evtq_thread
>>>>>>>        ret = arm_smmu_handle_evt
>>>>>>>            iommu_report_device_fault
>>>>>>>                iopf_param = iopf_get_dev_fault_param(dev);
>>>>>>>                // iopf is not enabled.
>>>>>>> // No RESUME will be sent!
>>>>>>>                if (WARN_ON(!iopf_param))
>>>>>>>                    return;
>>>>>>>        if (!ret || !__ratelimit(&rs))
>>>>>>>            continue;
>>>>>>>
>>>>>>> In this scenario, the io page-fault capability is not enabled.
>>>>>>> There are two problems here:
>>>>>>> 1. The event information is not printed.
>>>>>>> 2. The entire device(PF level) is stalled,not just the current
>>>>>>> VF. This affects other normal VFs.
>>>>>> Oh, so that stall is probably also due to b554e396e51c ("iommu: Make
>>>>>> iopf_group_response() return void"). I agree that we need a way to
>>>>>> propagate error handling back to the driver in the case that
>>>>>> 'iopf_param' is NULL, otherwise we're making the unexpected fault
>>>>>> considerably more problematic than it needs to be.
>>>>>>
>>>>>> Lu -- can we add the -ENODEV return back in the case that
>>>>>> iommu_report_device_fault() doesn't even find a 'iommu_fault_param' for
>>>>>> the device?
>>>>> Yes, of course. The commit b554e396e51c was added to consolidate the
>>>>> drivers' auto response code in the core with the assumption that driver
>>>>> only needs to call iommu_report_device_fault() for reporting an iopf.
>>>>>
>>>> I had a go at taking Jason's diff and implementing the suggestions in
>>>> this thread.
>>>> Kunkun -- please can you see if this fixes the problem for you?
>>> Okay, I'll test it as soon as I can.
>> It looks like the diff sent by Pranjal has whitespace mangling, so I
>> don't think you'll be able to apply it.
>>
>> Pranjal -- please can you send an unmangled version? If you want to test
>> out your mail setup, I'm happy to be a guinea pig so you don't spam the
>> mailing lists!
> Ugh, apologies for that, something went wrong with my client.
> Kunkun -- Please let me know if this fixes the problem.
> Lu -- It looks like the intel->page_response callback doesn't expect a
> NULL event, so, for now, I immediately return in that case. LMK what you
> think?

That's okay. We had such check there before the refactoring.

Thanks,
baolu