Re: [PATCH v3 13/16] iommu/intel-svm: notify page request to guest

Lu Baolu
2017-12-05T07:37:28Z

Hi,

On 11/18/2017 02:55 AM, Jacob Pan wrote:
> If the source device of a page request has its PASID table pointer
> bond to a guest, the first level page tables are owned by the guest.
> In this case, we shall let guest OS to manage page fault.
>
> This patch uses the IOMMU fault notification API to send notifications,
> possibly via VFIO, to the guest OS. Once guest pages are fault in, guest
> will issue page response which will be passed down via the invalidation
> passdown APIs.
>
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Signed-off-by: Ashok Raj <ashok.raj@intel.com>
> ---
> drivers/iommu/intel-svm.c | 80 ++++++++++++++++++++++++++++++++++++++++++-----
> include/linux/iommu.h | 1 +
> 2 files changed, 74 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/iommu/intel-svm.c b/drivers/iommu/intel-svm.c
> index f6697e5..77c25d8 100644
> --- a/drivers/iommu/intel-svm.c
> +++ b/drivers/iommu/intel-svm.c
> @@ -555,6 +555,71 @@ static bool is_canonical_address(u64 addr)
> return (((saddr << shift) >> shift) == saddr);
> }
>
> +static int prq_to_iommu_prot(struct page_req_dsc *req)
> +{
> + int prot = 0;
> +
> + if (req->rd_req)
> + prot |= IOMMU_FAULT_READ;
> + if (req->wr_req)
> + prot |= IOMMU_FAULT_WRITE;
> + if (req->exe_req)
> + prot |= IOMMU_FAULT_EXEC;
> + if (req->priv_req)
> + prot |= IOMMU_FAULT_PRIV;
> +
> + return prot;
> +}
> +
> +static int intel_svm_prq_report(struct device *dev, struct page_req_dsc *desc)
> +{
> + int ret = 0;

It seems that "ret" should be initialized as -EINVAL. Otherwise, this function
will return 0 for devices which have no fault handlers, and all page requests
will be ignored by iommu driver.

> + struct iommu_fault_event event;
> + struct pci_dev *pdev;
> +
> + /**
> + * If caller does not provide struct device, this is the case where
> + * guest PASID table is bound to the device. So we need to retrieve
> + * struct device from the page request descriptor then proceed.
> + */
> + if (!dev) {
> + pdev = pci_get_bus_and_slot(desc->bus, desc->devfn);
> + if (!pdev) {
> + pr_err("No PCI device found for PRQ [%02x:%02x.%d]\n",
> + desc->bus, PCI_SLOT(desc->devfn),
> + PCI_FUNC(desc->devfn));
> + return -ENODEV;
> + }
> + dev = &pdev->dev;
> + } else if (dev_is_pci(dev)) {
> + pdev = to_pci_dev(dev);
> + pci_dev_get(pdev);
> + } else
> + return -ENODEV;
> +
> + pr_debug("Notify PRQ device [%02x:%02x.%d]\n",
> + desc->bus, PCI_SLOT(desc->devfn),
> + PCI_FUNC(desc->devfn));
> +
> + /* invoke device fault handler if registered */
> + if (iommu_has_device_fault_handler(dev)) {
> + /* Fill in event data for device specific processing */
> + event.type = IOMMU_FAULT_PAGE_REQ;
> + event.addr = desc->addr;
> + event.pasid = desc->pasid;
> + event.page_req_group_id = desc->prg_index;
> + event.prot = prq_to_iommu_prot(desc);
> + event.last_req = desc->lpig;
> + event.pasid_valid = 1;
> + event.iommu_private = desc->private;
> + 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;
> @@ -578,7 +643,12 @@ static irqreturn_t prq_event_thread(int irq, void *d)
> handled = 1;
>
> req = &iommu->prq[head / sizeof(*req)];
> -
> + /**
> + * If prq is to be handled outside iommu driver via receiver of
> + * the fault notifiers, we skip the page response here.
> + */
> + if (!intel_svm_prq_report(NULL, req))
> + goto prq_advance;
> result = QI_RESP_FAILURE;
> address = (u64)req->addr << VTD_PAGE_SHIFT;
> if (!req->pasid_present) {
> @@ -649,11 +719,7 @@ static irqreturn_t prq_event_thread(int irq, void *d)
> if (WARN_ON(&sdev->list == &svm->devs))
> sdev = NULL;
>
> - if (sdev && sdev->ops && sdev->ops->fault_cb) {
> - int rwxp = (req->rd_req << 3) | (req->wr_req << 2) |
> - (req->exe_req << 1) | (req->priv_req);
> - sdev->ops->fault_cb(sdev->dev, req->pasid, req->addr, req->private, rwxp, result);
> - }
> + intel_svm_prq_report(sdev->dev, req);

Do you mind explaining why we need to report this request twice?

Best regards,
Lu Baolu

> /* We get here in the error case where the PASID lookup failed,
> and these can be NULL. Do not use them below this point! */
> sdev = NULL;
> @@ -679,7 +745,7 @@ static irqreturn_t prq_event_thread(int irq, void *d)
>
> qi_submit_sync(&resp, iommu);
> }
> -
> + prq_advance:
> head = (head + sizeof(*req)) & PRQ_RING_MASK;
> }
>
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 841c044..3083796b 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -42,6 +42,7 @@
> * if the IOMMU page table format is equivalent.
> */
> #define IOMMU_PRIV (1 << 5)
> +#define IOMMU_EXEC (1 << 6)
>
> struct iommu_ops;
> struct iommu_group;