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

[Baolu Lu]

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@xxxxxxxxxxxxxxx>  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