Re: [PATCH v2 3/4] iommu/vt-d: Report page request faults for guest SVA

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

Hi Kevin,

On 2020/7/6 9:29, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@linux.intel.com>
>> Sent: Monday, July 6, 2020 8:26 AM
>>
>> A pasid might be bound to a page table from a VM guest via the iommu
>> ops.sva_bind_gpasid. In this case, when a DMA page fault is detected
>> on the physical IOMMU, we need to inject the page fault request into
>> the guest. After the guest completes handling the page fault, a page
>> response need to be sent back via the iommu ops.page_response().
>>
>> This adds support to report a page request fault. Any external module
>> which is interested in handling this fault should regiester a notifier
>> callback.
> 
> be specific on which notifier to be registered...

Sure.

> 
>>
>> Co-developed-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
>> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
>> Co-developed-by: Liu Yi L <yi.l.liu@intel.com>
>> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>> ---
>>   drivers/iommu/intel/svm.c | 99 ++++++++++++++++++++++++++++++++-------
>>   1 file changed, 81 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
>> index c23167877b2b..08c58c2b1a06 100644
>> --- a/drivers/iommu/intel/svm.c
>> +++ b/drivers/iommu/intel/svm.c
>> @@ -815,6 +815,57 @@ static void intel_svm_drain_prq(struct device *dev,
>> int pasid)
>>   	}
>>   }
>>
>> +static int prq_to_iommu_prot(struct page_req_dsc *req)
>> +{
>> +	int prot = 0;
>> +
>> +	if (req->rd_req)
>> +		prot |= IOMMU_FAULT_PERM_READ;
>> +	if (req->wr_req)
>> +		prot |= IOMMU_FAULT_PERM_WRITE;
>> +	if (req->exe_req)
>> +		prot |= IOMMU_FAULT_PERM_EXEC;
>> +	if (req->pm_req)
>> +		prot |= IOMMU_FAULT_PERM_PRIV;
>> +
>> +	return prot;
>> +}
>> +
>> +static int
>> +intel_svm_prq_report(struct device *dev, struct page_req_dsc *desc)
>> +{
>> +	struct iommu_fault_event event;
>> +	u8 bus, devfn;
>> +
>> +	memset(&event, 0, sizeof(struct iommu_fault_event));
>> +	bus = PCI_BUS_NUM(desc->rid);
>> +	devfn = desc->rid & 0xff;
> 
> not required.

Yes. Will remove them.

> 
>> +
>> +	/* Fill in event data for device specific processing */
>> +	event.fault.type = IOMMU_FAULT_PAGE_REQ;
>> +	event.fault.prm.addr = desc->addr;
>> +	event.fault.prm.pasid = desc->pasid;
>> +	event.fault.prm.grpid = desc->prg_index;
>> +	event.fault.prm.perm = prq_to_iommu_prot(desc);
>> +
>> +	/*
>> +	 * Set last page in group bit if private data is present,
>> +	 * page response is required as it does for LPIG.
>> +	 */
> 
> move to priv_data_present check?

Yes.

> 
>> +	if (desc->lpig)
>> +		event.fault.prm.flags |=
>> IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE;
>> +	if (desc->pasid_present)
>> +		event.fault.prm.flags |=
>> IOMMU_FAULT_PAGE_REQUEST_PASID_VALID;
>> +	if (desc->priv_data_present) {
>> +		event.fault.prm.flags |=
>> IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE;
>> +		event.fault.prm.flags |=
>> IOMMU_FAULT_PAGE_REQUEST_PRIV_DATA;
>> +		memcpy(event.fault.prm.private_data, desc->priv_data,
>> +		       sizeof(desc->priv_data));
>> +	}
>> +
>> +	return iommu_report_device_fault(dev, &event);
>> +}
>> +
>>   static irqreturn_t prq_event_thread(int irq, void *d)
>>   {
>>   	struct intel_iommu *iommu = d;
>> @@ -828,7 +879,7 @@ static irqreturn_t prq_event_thread(int irq, void *d)
>>   	tail = dmar_readq(iommu->reg + DMAR_PQT_REG) &
>> PRQ_RING_MASK;
>>   	head = dmar_readq(iommu->reg + DMAR_PQH_REG) &
>> PRQ_RING_MASK;
>>   	while (head != tail) {
>> -		struct intel_svm_dev *sdev;
>> +		struct intel_svm_dev *sdev = NULL;
> 
> move to outside of the loop, otherwise later check always hit "if (!sdev)"

Yes, good catch!

> 
>>   		struct vm_area_struct *vma;
>>   		struct page_req_dsc *req;
>>   		struct qi_desc resp;
>> @@ -864,6 +915,20 @@ static irqreturn_t prq_event_thread(int irq, void *d)
>>   			}
>>   		}
>>
>> +		if (!sdev || sdev->sid != req->rid) {
>> +			struct intel_svm_dev *t;
>> +
>> +			sdev = NULL;
>> +			rcu_read_lock();
>> +			list_for_each_entry_rcu(t, &svm->devs, list) {
>> +				if (t->sid == req->rid) {
>> +					sdev = t;
>> +					break;
>> +				}
>> +			}
>> +			rcu_read_unlock();
>> +		}
>> +
>>   		result = QI_RESP_INVALID;
>>   		/* Since we're using init_mm.pgd directly, we should never
>> take
>>   		 * any faults on kernel addresses. */
>> @@ -874,6 +939,17 @@ static irqreturn_t prq_event_thread(int irq, void *d)
>>   		if (!is_canonical_address(address))
>>   			goto bad_req;
>>
>> +		/*
>> +		 * If prq is to be handled outside iommu driver via receiver of
>> +		 * the fault notifiers, we skip the page response here.
>> +		 */
>> +		if (svm->flags & SVM_FLAG_GUEST_MODE) {
>> +			if (sdev && !intel_svm_prq_report(sdev->dev, req))
>> +				goto prq_advance;
>> +			else
>> +				goto bad_req;
>> +		}
>> +
>>   		/* If the mm is already defunct, don't handle faults. */
>>   		if (!mmget_not_zero(svm->mm))
>>   			goto bad_req;
>> @@ -892,24 +968,10 @@ static irqreturn_t prq_event_thread(int irq, void *d)
>>   			goto invalid;
>>
>>   		result = QI_RESP_SUCCESS;
>> -	invalid:
>> +invalid:
>>   		mmap_read_unlock(svm->mm);
>>   		mmput(svm->mm);
>> -	bad_req:
>> -		/* Accounting for major/minor faults? */
>> -		rcu_read_lock();
>> -		list_for_each_entry_rcu(sdev, &svm->devs, list) {
>> -			if (sdev->sid == req->rid)
>> -				break;
>> -		}
>> -		/* Other devices can go away, but the drivers are not
>> permitted
>> -		 * to unbind while any page faults might be in flight. So it's
>> -		 * OK to drop the 'lock' here now we have it. */
> 
> should we keep and move this comment to earlier sdev lookup? and

I thought this comment explained why rcu_read_unlock() before the next
checking. In the new lookup code, we don't need to check, hence I
removed the comments.

> regarding to guest unbind, ae we preventing the fault owner (outside
> of iommu driver) to unbind against in-flight fault request?

Yes. We always wait until all prq with the same pasid completes in
gpasid_unbind().

> 
>> -		rcu_read_unlock();
>> -
>> -		if (WARN_ON(&sdev->list == &svm->devs))
>> -			sdev = NULL;
> 
> similarly should we keep the WARN_ON check here?

Yes, agreed. We can keep a WARN_ON() here.

> 
>> -
>> +bad_req:
>>   		if (sdev && sdev->ops && sdev->ops->fault_cb) {
>>   			int rwxp = (req->rd_req << 3) | (req->wr_req << 2) |
>>   				(req->exe_req << 1) | (req->pm_req);
>> @@ -920,7 +982,7 @@ static irqreturn_t prq_event_thread(int irq, void *d)
>>   		   and these can be NULL. Do not use them below this point!
>> */
>>   		sdev = NULL;
>>   		svm = NULL;
>> -	no_pasid:
>> +no_pasid:
>>   		if (req->lpig || req->priv_data_present) {
>>   			/*
>>   			 * Per VT-d spec. v3.0 ch7.7, system software must
>> @@ -945,6 +1007,7 @@ static irqreturn_t prq_event_thread(int irq, void *d)
>>   			resp.qw3 = 0;
>>   			qi_submit_sync(iommu, &resp, 1, 0);
>>   		}
>> +prq_advance:
>>   		head = (head + sizeof(*req)) & PRQ_RING_MASK;
>>   	}
>>
>> --
>> 2.17.1
> 
> Thanks
> Kevin
> 

Best regards,
baolu
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