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

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Message-ID: <20240805123001.GB9326@willie-the-truck>
Date: Mon, 5 Aug 2024 13:30:01 +0100
From: Will Deacon <will@...nel.org>
To: Kunkun Jiang <jiangkunkun@...wei.com>
Cc: Pranjal Shrivastava <praan@...gle.com>,
	Baolu Lu <baolu.lu@...ux.intel.com>,
	Robin Murphy <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>,
	Jason Gunthorpe <jgg@...pe.ca>, Nicolin Chen <nicolinc@...dia.com>,
	Michael Shavit <mshavit@...gle.com>,
	Mostafa Saleh <smostafa@...gle.com>,
	"moderated list:ARM SMMU DRIVERS" <linux-arm-kernel@...ts.infradead.org>,
	iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
	wanghaibin.wang@...wei.com, yuzenghui@...wei.com,
	tangnianyao@...wei.com
Subject: Re: [bug report] iommu/arm-smmu-v3: Event cannot be printed in some
 scenarios

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@...ux.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!

Cheers,

Will