Re: [PATCH v3 4/4] iommu/vt-d: Add page response ops support

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

Hi Kevin,

On 2020/7/10 13:49, Tian, Kevin wrote:
>> From: Lu Baolu<baolu.lu@linux.intel.com>
>> Sent: Friday, July 10, 2020 1:37 PM
>>
>> Hi Kevin,
>>
>> On 2020/7/10 10:42, Tian, Kevin wrote:
>>>> From: Lu Baolu<baolu.lu@linux.intel.com>
>>>> Sent: Thursday, July 9, 2020 3:06 PM
>>>>
>>>> After page requests are handled, software must respond to the device
>>>> which raised the page request with the result. This is done through
>>>> the iommu ops.page_response if the request was reported to outside of
>>>> vendor iommu driver through iommu_report_device_fault(). This adds
>> the
>>>> VT-d implementation of page_response ops.
>>>>
>>>> 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/iommu.c |   1 +
>>>>    drivers/iommu/intel/svm.c   | 100
>>>> ++++++++++++++++++++++++++++++++++++
>>>>    include/linux/intel-iommu.h |   3 ++
>>>>    3 files changed, 104 insertions(+)
>>>>
>>>> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
>>>> index 4a6b6960fc32..98390a6d8113 100644
>>>> --- a/drivers/iommu/intel/iommu.c
>>>> +++ b/drivers/iommu/intel/iommu.c
>>>> @@ -6057,6 +6057,7 @@ const struct iommu_ops intel_iommu_ops = {
>>>>    	.sva_bind		= intel_svm_bind,
>>>>    	.sva_unbind		= intel_svm_unbind,
>>>>    	.sva_get_pasid		= intel_svm_get_pasid,
>>>> +	.page_response		= intel_svm_page_response,
>>>>    #endif
>>>>    };
>>>>
>>>> diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
>>>> index d24e71bac8db..839d2af377b6 100644
>>>> --- a/drivers/iommu/intel/svm.c
>>>> +++ b/drivers/iommu/intel/svm.c
>>>> @@ -1082,3 +1082,103 @@ int intel_svm_get_pasid(struct iommu_sva
>> *sva)
>>>>    	return pasid;
>>>>    }
>>>> +
>>>> +int intel_svm_page_response(struct device *dev,
>>>> +			    struct iommu_fault_event *evt,
>>>> +			    struct iommu_page_response *msg)
>>>> +{
>>>> +	struct iommu_fault_page_request *prm;
>>>> +	struct intel_svm_dev *sdev = NULL;
>>>> +	struct intel_svm *svm = NULL;
>>>> +	struct intel_iommu *iommu;
>>>> +	bool private_present;
>>>> +	bool pasid_present;
>>>> +	bool last_page;
>>>> +	u8 bus, devfn;
>>>> +	int ret = 0;
>>>> +	u16 sid;
>>>> +
>>>> +	if (!dev || !dev_is_pci(dev))
>>>> +		return -ENODEV;
>>>> +
>>>> +	iommu = device_to_iommu(dev, &bus, &devfn);
>>>> +	if (!iommu)
>>>> +		return -ENODEV;
>>>> +
>>>> +	if (!msg || !evt)
>>>> +		return -EINVAL;
>>>> +
>>>> +	mutex_lock(&pasid_mutex);
>>>> +
>>>> +	prm = &evt->fault.prm;
>>>> +	sid = PCI_DEVID(bus, devfn);
>>>> +	pasid_present = prm->flags &
>>>> IOMMU_FAULT_PAGE_REQUEST_PASID_VALID;
>>>> +	private_present = prm->flags &
>>>> IOMMU_FAULT_PAGE_REQUEST_PRIV_DATA;
>>>> +	last_page = prm->flags &
>>>> IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE;
>>>> +
>>>> +	if (pasid_present) {
>>>> +		if (prm->pasid == 0 || prm->pasid >= PASID_MAX) {
>>>> +			ret = -EINVAL;
>>>> +			goto out;
>>>> +		}
>>>> +
>>>> +		ret = pasid_to_svm_sdev(dev, prm->pasid, &svm, &sdev);
>>>> +		if (ret || !sdev) {
>>>> +			ret = -ENODEV;
>>>> +			goto out;
>>>> +		}
>>>> +
>>>> +		/*
>>>> +		 * For responses from userspace, need to make sure that the
>>>> +		 * pasid has been bound to its mm.
>>>> +		*/
>>>> +		if (svm->flags & SVM_FLAG_GUEST_MODE) {
>>>> +			struct mm_struct *mm;
>>>> +
>>>> +			mm = get_task_mm(current);
>>>> +			if (!mm) {
>>>> +				ret = -EINVAL;
>>>> +				goto out;
>>>> +			}
>>>> +
>>>> +			if (mm != svm->mm) {
>>>> +				ret = -ENODEV;
>>>> +				mmput(mm);
>>>> +				goto out;
>>>> +			}
>>>> +
>>>> +			mmput(mm);
>>>> +		}
>>>> +	} else {
>>>> +		pr_err_ratelimited("Invalid page response: no pasid\n");
>>>> +		ret = -EINVAL;
>>>> +		goto out;
>>> check pasid=0 first, then no need to indent so many lines above.
>> Yes.
>>
>>>> +	}
>>>> +
>>>> +	/*
>>>> +	 * Per VT-d spec. v3.0 ch7.7, system software must respond
>>>> +	 * with page group response if private data is present (PDP)
>>>> +	 * or last page in group (LPIG) bit is set. This is an
>>>> +	 * additional VT-d requirement beyond PCI ATS spec.
>>>> +	 */
>>> What is the behavior if system software doesn't follow the requirement?
>>> en... maybe the question is really about whether the information in prm
>>> comes from userspace or from internally-recorded info in iommu core.
>>> The former cannot be trusted. The latter one is OK.
>> We require a page response when reporting such event. The upper layer
>> (IOMMU core or VFIO) will be implemented with a timer, if userspace
>> doesn't respond in time, the timer will get expired and a FAILURE
>> response will be sent to device.
> Yes, timer helps when userspace doesn't respond. Then I'm fine with
> this patch.
> 
> Reviewed-by: Kevin Tian<kevin.tian@intel.com>
> 
> btw when you say IOMMU core or VFIO, does it mean the timer mechanism
> is not implemented yet?
> 

It's in local tree, not upstream yet.

Best regards,
baolu
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