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

["Tian, Kevin" <kevin.tian@intel.com>]

> From: Lu Baolu <baolu.lu@linux.intel.com>
> Sent: Sunday, June 28, 2020 8:34 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.
> 
> 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 | 83
> +++++++++++++++++++++++++++++++++++++--
>  1 file changed, 80 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
> index c23167877b2b..4800bb6f8794 100644
> --- a/drivers/iommu/intel/svm.c
> +++ b/drivers/iommu/intel/svm.c
> @@ -815,6 +815,69 @@ 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 intel_iommu *iommu, struct page_req_dsc
> *desc)
> +{
> +	struct iommu_fault_event event;
> +	struct pci_dev *pdev;
> +	u8 bus, devfn;
> +	int ret = 0;
> +
> +	memset(&event, 0, sizeof(struct iommu_fault_event));
> +	bus = PCI_BUS_NUM(desc->rid);
> +	devfn = desc->rid & 0xff;
> +	pdev = pci_get_domain_bus_and_slot(iommu->segment, bus, devfn);

Is this step necessary? dev can be passed in (based on sdev), and more
importantly iommu_report_device_fault already handles the ref counting
e.g. get_device(dev) when fault handler is valid...

> +
> +	if (!pdev) {
> +		pr_err("No PCI device found for PRQ [%02x:%02x.%d]\n",
> +		       bus, PCI_SLOT(devfn), PCI_FUNC(devfn));
> +		return -ENODEV;
> +	}
> +
> +	/* 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.
> +	 */
> +	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;

why setting lpig under this condition? 

> +		event.fault.prm.flags |=
> IOMMU_FAULT_PAGE_REQUEST_PRIV_DATA;
> +		memcpy(event.fault.prm.private_data, desc->priv_data,
> +		       sizeof(desc->priv_data));
> +	}
> +
> +	ret = iommu_report_device_fault(&pdev->dev, &event);
> +	pci_dev_put(pdev);
> +
> +	return ret;
> +}
> +
>  static irqreturn_t prq_event_thread(int irq, void *d)
>  {
>  	struct intel_iommu *iommu = d;
> @@ -874,6 +937,19 @@ 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) {
> +			int res = intel_svm_prq_report(iommu, req);
> +
> +			if (!res)
> +				goto prq_advance;
> +			else
> +				goto bad_req;
> +		}
> +

I noted in bad_req there is another reporting logic:

                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);
                        sdev->ops->fault_cb(sdev->dev, req->pasid, req->addr,
                                            req->priv_data, rwxp, result);
                }

It was introduced in the 1st version of svm.c. It might be unrelated to
this patch, but I wonder whether that one should be replaced with 
iommu_report_device_fault too?

Thanks
Kevin

>  		/* If the mm is already defunct, don't handle faults. */
>  		if (!mmget_not_zero(svm->mm))
>  			goto bad_req;
> @@ -892,10 +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:
> +bad_req:
>  		/* Accounting for major/minor faults? */
>  		rcu_read_lock();
>  		list_for_each_entry_rcu(sdev, &svm->devs, list) {
> @@ -920,7 +996,7 @@ 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 +1021,7 @@ 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

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