iommu: Allow page responses without PASID

Some PCIe devices do not expect a PASID value in PRI Page Responses.
If the "PRG Response PASID Required" bit in the PRI capability is zero,
then the OS should not set the PASID field. Similarly on Arm SMMU,
responses to stall events do not have a PASID.

Currently iommu_page_response() systematically checks that the PASID in
the page response corresponds to the one in the page request. This can't
work with virtualization because a page response coming from a guest OS
won't have a PASID if the passed-through device does not require one.

Add a flag to page requests that declares whether the corresponding
response needs to have a PASID. When this flag isn't set, allow page
responses without PASID.
Reported-by: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Link: https://lore.kernel.org/r/20200616144712.748818-1-jean-philippe@linaro.orgSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/iommu.c

@@ -1185,11 +1185,12 @@ EXPORT_SYMBOL_GPL(iommu_report_device_fault);
 int iommu_page_response(struct device *dev,
 			struct iommu_page_response *msg)
 {
-	bool pasid_valid;
+	bool needs_pasid;
 	int ret = -EINVAL;
 	struct iommu_fault_event *evt;
 	struct iommu_fault_page_request *prm;
 	struct dev_iommu *param = dev->iommu;
+	bool has_pasid = msg->flags & IOMMU_PAGE_RESP_PASID_VALID;
 	struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
 
 	if (!domain || !domain->ops->page_response)
@@ -1214,14 +1215,24 @@ int iommu_page_response(struct device *dev,
 	 */
 	list_for_each_entry(evt, &param->fault_param->faults, list) {
 		prm = &evt->fault.prm;
-		pasid_valid = prm->flags & IOMMU_FAULT_PAGE_REQUEST_PASID_VALID;
+		if (prm->grpid != msg->grpid)
+			continue;
 
-		if ((pasid_valid && prm->pasid != msg->pasid) ||
-		    prm->grpid != msg->grpid)
+		/*
+		 * If the PASID is required, the corresponding request is
+		 * matched using the group ID, the PASID valid bit and the PASID
+		 * value. Otherwise only the group ID matches request and
+		 * response.
+		 */
+		needs_pasid = prm->flags & IOMMU_FAULT_PAGE_RESPONSE_NEEDS_PASID;
+		if (needs_pasid && (!has_pasid || msg->pasid != prm->pasid))
 			continue;
 
-		/* Sanitize the reply */
-		msg->flags = pasid_valid ? IOMMU_PAGE_RESP_PASID_VALID : 0;
+		if (!needs_pasid && has_pasid) {
+			/* No big deal, just clear it. */
+			msg->flags &= ~IOMMU_PAGE_RESP_PASID_VALID;
+			msg->pasid = 0;
+		}
 
 		ret = domain->ops->page_response(dev, evt, msg);
 		list_del(&evt->list);

include/uapi/linux/iommu.h

@@ -81,7 +81,10 @@ struct iommu_fault_unrecoverable {
 /**
  * struct iommu_fault_page_request - Page Request data
  * @flags: encodes whether the corresponding fields are valid and whether this
- *         is the last page in group (IOMMU_FAULT_PAGE_REQUEST_* values)
+ *         is the last page in group (IOMMU_FAULT_PAGE_REQUEST_* values).
+ *         When IOMMU_FAULT_PAGE_RESPONSE_NEEDS_PASID is set, the page response
+ *         must have the same PASID value as the page request. When it is clear,
+ *         the page response should not have a PASID.
  * @pasid: Process Address Space ID
  * @grpid: Page Request Group Index
  * @perm: requested page permissions (IOMMU_FAULT_PERM_* values)
@@ -92,6 +95,7 @@ struct iommu_fault_page_request {
 #define IOMMU_FAULT_PAGE_REQUEST_PASID_VALID	(1 << 0)
 #define IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE	(1 << 1)
 #define IOMMU_FAULT_PAGE_REQUEST_PRIV_DATA	(1 << 2)
+#define IOMMU_FAULT_PAGE_RESPONSE_NEEDS_PASID	(1 << 3)
 	__u32	flags;
 	__u32	pasid;
 	__u32	grpid;