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

Pranjal Shrivastava
2024-08-05T15:33:02Z

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?

Here's the updated diff:
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index a31460f9f3d4..ed2b106e02dd 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -1777,7 +1777,7 @@ static int arm_smmu_handle_evt(struct arm_smmu_device *smmu, u64 *evt)
goto out_unlock;
}

- iommu_report_device_fault(master->dev, &fault_evt);
+ ret = iommu_report_device_fault(master->dev, &fault_evt);
out_unlock:
mutex_unlock(&smmu->streams_mutex);
return ret;
diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
index 0e3a9b38bef2..7684e7562584 100644
--- a/drivers/iommu/intel/svm.c
+++ b/drivers/iommu/intel/svm.c
@@ -532,6 +532,9 @@ void intel_svm_page_response(struct device *dev, struct iopf_fault *evt,
bool last_page;
u16 sid;

+ if (!evt)
+ return;
+
prm = &evt->fault.prm;
sid = PCI_DEVID(bus, devfn);
pasid_present = prm->flags & IOMMU_FAULT_PAGE_REQUEST_PASID_VALID;
diff --git a/drivers/iommu/io-pgfault.c b/drivers/iommu/io-pgfault.c
index 7c9011992d3f..0c3b2125563e 100644
--- a/drivers/iommu/io-pgfault.c
+++ b/drivers/iommu/io-pgfault.c
@@ -113,6 +113,57 @@ static struct iopf_group *iopf_group_alloc(struct iommu_fault_param *iopf_param,
return group;
}

+static struct iommu_attach_handle *find_fault_handler(struct device *dev,
+ struct iopf_fault *evt)
+{
+ struct iommu_fault *fault = &evt->fault;
+ struct iommu_attach_handle *attach_handle;
+
+ if (fault->prm.flags & IOMMU_FAULT_PAGE_REQUEST_PASID_VALID) {
+ attach_handle = iommu_attach_handle_get(dev->iommu_group,
+ fault->prm.pasid, 0);
+ if (IS_ERR(attach_handle)) {
+ const struct iommu_ops *ops = dev_iommu_ops(dev);
+
+ if (!ops->user_pasid_table)
+ return NULL;
+
+ /*
+ * The iommu driver for this device supports user-
+ * managed PASID table. Therefore page faults for
+ * any PASID should go through the NESTING domain
+ * attached to the device RID.
+ */
+ attach_handle = iommu_attach_handle_get(
+ dev->iommu_group, IOMMU_NO_PASID,
+ IOMMU_DOMAIN_NESTED);
+ if (IS_ERR(attach_handle))
+ return NULL;
+ }
+ } else {
+ attach_handle = iommu_attach_handle_get(dev->iommu_group,
+ IOMMU_NO_PASID, 0);
+ if (IS_ERR(attach_handle))
+ return NULL;
+ }
+
+ if (!attach_handle->domain->iopf_handler)
+ return NULL;
+ return attach_handle;
+}
+
+static void iopf_error_response(struct device *dev, struct iommu_fault *fault)
+{
+ const struct iommu_ops *ops = dev_iommu_ops(dev);
+ struct iommu_page_response resp = {
+ .pasid = fault->prm.pasid,
+ .grpid = fault->prm.grpid,
+ .code = IOMMU_PAGE_RESP_INVALID
+ };
+
+ ops->page_response(dev, NULL, &resp);
+}
+
/**
* iommu_report_device_fault() - Report fault event to device driver
* @dev: the device
@@ -153,16 +204,25 @@ static struct iopf_group *iopf_group_alloc(struct iommu_fault_param *iopf_param,
* hardware has been set to block the page faults) and the pending page faults
* have been flushed.
*/
-void iommu_report_device_fault(struct device *dev, struct iopf_fault *evt)
+int iommu_report_device_fault(struct device *dev, struct iopf_fault *evt)
{
+ struct iommu_attach_handle *attach_handle;
struct iommu_fault *fault = &evt->fault;
struct iommu_fault_param *iopf_param;
struct iopf_group abort_group = {};
struct iopf_group *group;

+ attach_handle = find_fault_handler(dev, evt);
+ if (!attach_handle)
+ goto err_bad_iopf;
+
+ /*
+ * Something has gone wrong if a fault capable domain is attached but no
+ * iopf_param is setup
+ */
iopf_param = iopf_get_dev_fault_param(dev);
if (WARN_ON(!iopf_param))
- return;
+ goto err_bad_iopf;

if (!(fault->prm.flags & IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE)) {
report_partial_fault(iopf_param, fault);
@@ -182,38 +242,7 @@ void iommu_report_device_fault(struct device *dev, struct iopf_fault *evt)
if (group == &abort_group)
goto err_abort;

- if (fault->prm.flags & IOMMU_FAULT_PAGE_REQUEST_PASID_VALID) {
- group->attach_handle = iommu_attach_handle_get(dev->iommu_group,
- fault->prm.pasid,
- 0);
- if (IS_ERR(group->attach_handle)) {
- const struct iommu_ops *ops = dev_iommu_ops(dev);
-
- if (!ops->user_pasid_table)
- goto err_abort;
-
- /*
- * The iommu driver for this device supports user-
- * managed PASID table. Therefore page faults for
- * any PASID should go through the NESTING domain
- * attached to the device RID.
- */
- group->attach_handle =
- iommu_attach_handle_get(dev->iommu_group,
- IOMMU_NO_PASID,
- IOMMU_DOMAIN_NESTED);
- if (IS_ERR(group->attach_handle))
- goto err_abort;
- }
- } else {
- group->attach_handle =
- iommu_attach_handle_get(dev->iommu_group, IOMMU_NO_PASID, 0);
- if (IS_ERR(group->attach_handle))
- goto err_abort;
- }
-
- if (!group->attach_handle->domain->iopf_handler)
- goto err_abort;
+ group->attach_handle = attach_handle;

/*
* On success iopf_handler must call iopf_group_response() and
@@ -222,7 +251,7 @@ void iommu_report_device_fault(struct device *dev, struct iopf_fault *evt)
if (group->attach_handle->domain->iopf_handler(group))
goto err_abort;

- return;
+ return 0;

err_abort:
dev_warn_ratelimited(dev, "iopf with pasid %d aborted\n",
@@ -232,6 +261,14 @@ void iommu_report_device_fault(struct device *dev, struct iopf_fault *evt)
__iopf_free_group(group);
else
iopf_free_group(group);
+
+ return 0;
+
+err_bad_iopf:
+ if (fault->type == IOMMU_FAULT_PAGE_REQ)
+ iopf_error_response(dev, fault);
+
+ return -EINVAL;
}
EXPORT_SYMBOL_GPL(iommu_report_device_fault);

diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index d87f9cbfc01e..062156a8d87b 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -1561,7 +1561,7 @@ struct iopf_queue *iopf_queue_alloc(const char *name);
void iopf_queue_free(struct iopf_queue *queue);
int iopf_queue_discard_partial(struct iopf_queue *queue);
void iopf_free_group(struct iopf_group *group);
-void iommu_report_device_fault(struct device *dev, struct iopf_fault *evt);
+int iommu_report_device_fault(struct device *dev, struct iopf_fault *evt);
void iopf_group_response(struct iopf_group *group,
enum iommu_page_response_code status);
#else
@@ -1599,9 +1599,10 @@ static inline void iopf_free_group(struct iopf_group *group)
{
}

-static inline void
+static inline int
iommu_report_device_fault(struct device *dev, struct iopf_fault *evt)
{
+ return -ENODEV;
}

static inline void iopf_group_response(struct iopf_group *group,

>
> Cheers,
>
> Will

Thanks,
Pranjal