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Date:   Mon, 6 Jul 2020 15:47:58 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/4] iommu/vt-d: Report page request faults for guest
 SVA

On 2020/7/6 9:36, Tian, Kevin wrote:
>> From: Tian, Kevin
>> Sent: Monday, July 6, 2020 9:30 AM
>>
>>> From: Lu Baolu <baolu.lu@...ux.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...
>>
>>>
>>> Co-developed-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
>>> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
>>> Co-developed-by: Liu Yi L <yi.l.liu@...el.com>
>>> Signed-off-by: Liu Yi L <yi.l.liu@...el.com>
>>> Signed-off-by: Lu Baolu <baolu.lu@...ux.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.
>>
>>> +
>>> +	/* 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?
>>
>>> +	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;
> 
> btw earlier comment is more about the behavior of the fault
> handler (e.g. the guest), but not about why we need convert
> to last_page prm flag. Let's make it clear that doing so is
> because iommu_report_device_fault doesn't understand this
> vt-d specific requirement thus we set last_page as a workaround.

Yes. I will add this in the comment.

Best regards,
baolu

> 
> Thanks
> Kevin
> 
>>> +		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)"
>>
>>>   		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
>> regarding to guest unbind, ae we preventing the fault owner (outside
>> of iommu driver) to unbind against in-flight fault request?
>>
>>> -		rcu_read_unlock();
>>> -
>>> -		if (WARN_ON(&sdev->list == &svm->devs))
>>> -			sdev = NULL;
>>
>> similarly should we keep the WARN_ON check 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

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