iommufd: Change the order of MSI setup

Eric points out this is wrong for the rare case of someone using
allow_unsafe_interrupts on ARM. We always have to setup the MSI window in
the domain if the iommu driver asks for it.

Move the iommu_get_msi_cookie() setup to the top of the function and
always do it, regardless of the security mode. Add checks to
iommufd_device_setup_msi() to ensure the driver is not doing something
incomprehensible. No current driver will set both a HW and SW MSI window,
or have more than one SW MSI window.

Fixes: e8d5721 ("iommufd: Add kAPI toward external drivers for physical devices")
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Kevin Tian <[email protected]>
Reported-by: Eric Auger <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>

Author: jgunthorpe

drivers/iommu/iommufd/device.c

@@ -139,53 +139,47 @@ static int iommufd_device_setup_msi(struct iommufd_device *idev,
 	int rc;
 
 	/*
-	 * IOMMU_CAP_INTR_REMAP means that the platform is isolating MSI, and it
-	 * creates the MSI window by default in the iommu domain. Nothing
-	 * further to do.
-	 */
-	if (device_iommu_capable(idev->dev, IOMMU_CAP_INTR_REMAP))
-		return 0;
-
-	/*
-	 * On ARM systems that set the global IRQ_DOMAIN_FLAG_MSI_REMAP every
-	 * allocated iommu_domain will block interrupts by default and this
-	 * special flow is needed to turn them back on. iommu_dma_prepare_msi()
-	 * will install pages into our domain after request_irq() to make this
-	 * work.
+	 * If the IOMMU driver gives a IOMMU_RESV_SW_MSI then it is asking us to
+	 * call iommu_get_msi_cookie() on its behalf. This is necessary to setup
+	 * the MSI window so iommu_dma_prepare_msi() can install pages into our
+	 * domain after request_irq(). If it is not done interrupts will not
+	 * work on this domain.
 	 *
 	 * FIXME: This is conceptually broken for iommufd since we want to allow
 	 * userspace to change the domains, eg switch from an identity IOAS to a
 	 * DMA IOAS. There is currently no way to create a MSI window that
 	 * matches what the IRQ layer actually expects in a newly created
 	 * domain.
 	 */
-	if (irq_domain_check_msi_remap()) {
-		if (WARN_ON(!sw_msi_start))
-			return -EPERM;
+	if (sw_msi_start != PHYS_ADDR_MAX && !hwpt->msi_cookie) {
+		rc = iommu_get_msi_cookie(hwpt->domain, sw_msi_start);
+		if (rc)
+			return rc;
+
 		/*
 		 * iommu_get_msi_cookie() can only be called once per domain,
 		 * it returns -EBUSY on later calls.
 		 */
-		if (hwpt->msi_cookie)
-			return 0;
-		rc = iommu_get_msi_cookie(hwpt->domain, sw_msi_start);
-		if (rc)
-			return rc;
 		hwpt->msi_cookie = true;
-		return 0;
 	}
 
 	/*
-	 * Otherwise the platform has a MSI window that is not isolated. For
-	 * historical compat with VFIO allow a module parameter to ignore the
-	 * insecurity.
+	 * For historical compat with VFIO the insecure interrupt path is
+	 * allowed if the module parameter is set. Insecure means that a MemWr
+	 * operation from the device (eg a simple DMA) cannot trigger an
+	 * interrupt outside this iommufd context.
 	 */
-	if (!allow_unsafe_interrupts)
-		return -EPERM;
+	if (!device_iommu_capable(idev->dev, IOMMU_CAP_INTR_REMAP) &&
+	    !irq_domain_check_msi_remap()) {
+		if (!allow_unsafe_interrupts)
+			return -EPERM;
 
-	dev_warn(
-		idev->dev,
-		"MSI interrupt window cannot be isolated by the IOMMU, this platform is insecure. Use the \"allow_unsafe_interrupts\" module parameter to override\n");
+		dev_warn(
+			idev->dev,
+			"MSI interrupts are not secure, they cannot be isolated by the platform. "
+			"Check that platform features like interrupt remapping are enabled. "
+			"Use the \"allow_unsafe_interrupts\" module parameter to override\n");
+	}
 	return 0;
 }
 
@@ -203,7 +197,7 @@ static bool iommufd_hw_pagetable_has_group(struct iommufd_hw_pagetable *hwpt,
 static int iommufd_device_do_attach(struct iommufd_device *idev,
 				    struct iommufd_hw_pagetable *hwpt)
 {
-	phys_addr_t sw_msi_start = 0;
+	phys_addr_t sw_msi_start = PHYS_ADDR_MAX;
 	int rc;
 
 	mutex_lock(&hwpt->devices_lock);

drivers/iommu/iommufd/io_pagetable.c

@@ -1170,6 +1170,8 @@ int iopt_table_enforce_group_resv_regions(struct io_pagetable *iopt,
 	struct iommu_resv_region *resv;
 	struct iommu_resv_region *tmp;
 	LIST_HEAD(group_resv_regions);
+	unsigned int num_hw_msi = 0;
+	unsigned int num_sw_msi = 0;
 	int rc;
 
 	down_write(&iopt->iova_rwsem);
@@ -1181,23 +1183,25 @@ int iopt_table_enforce_group_resv_regions(struct io_pagetable *iopt,
 		if (resv->type == IOMMU_RESV_DIRECT_RELAXABLE)
 			continue;
 
-		/*
-		 * The presence of any 'real' MSI regions should take precedence
-		 * over the software-managed one if the IOMMU driver happens to
-		 * advertise both types.
-		 */
-		if (sw_msi_start && resv->type == IOMMU_RESV_MSI) {
-			*sw_msi_start = 0;
-			sw_msi_start = NULL;
-		}
-		if (sw_msi_start && resv->type == IOMMU_RESV_SW_MSI)
+		if (sw_msi_start && resv->type == IOMMU_RESV_MSI)
+			num_hw_msi++;
+		if (sw_msi_start && resv->type == IOMMU_RESV_SW_MSI) {
 			*sw_msi_start = resv->start;
+			num_sw_msi++;
+		}
 
 		rc = iopt_reserve_iova(iopt, resv->start,
 				       resv->length - 1 + resv->start, device);
 		if (rc)
 			goto out_reserved;
 	}
+
+	/* Drivers must offer sane combinations of regions */
+	if (WARN_ON(num_sw_msi && num_hw_msi) || WARN_ON(num_sw_msi > 1)) {
+		rc = -EINVAL;
+		goto out_reserved;
+	}
+
 	rc = 0;
 	goto out_free_resv;