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Message-ID: <20240724102417.GA27376@willie-the-truck>
Date: Wed, 24 Jul 2024 11:24:17 +0100
From: Will Deacon <will@...nel.org>
To: Kunkun Jiang <jiangkunkun@...wei.com>
Cc: Lu Baolu <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 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?
Will
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