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

Jean-Philippe Brucker
2020-07-07T11:23:59Z

On Mon, Jul 06, 2020 at 08:25:34AM +0800, Lu Baolu wrote:
> 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>
> ---
[...]
> +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;
> +
> + /* 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;

Do you also need to set IOMMU_FAULT_PAGE_RESPONSE_NEEDS_PASID? I added
the flag to deal with devices that do not want a PASID value in their PRI
response (bit 15 in the PCIe Page Request Status Register):
https://lore.kernel.org/linux-iommu/20200616144712.748818-1-jean-philippe@linaro.org/
(applied by Joerg for v5.9)

Grepping for pci_prg_resp_pasid_required() in intel/iommu.c it seems to
currently reject devices that do not want a PASID in a PRI response, so I
think you can set this flag unconditionally for now.

Thanks,
Jean

> + 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);
> +}