[PATCH v5 05/25] iommu/iopf: Handle mm faults

[Jean-Philippe Brucker <jean-philippe@linaro.org>]

When a recoverable page fault is handled by the fault workqueue, find the
associated mm and call handle_mm_fault.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
---
v4->v5: no need to call mmput_async() anymore, since the MMU release()
        doesn't flush the IOPF queue anymore.
---
 drivers/iommu/io-pgfault.c | 77 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 75 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/io-pgfault.c b/drivers/iommu/io-pgfault.c
index 5bba8e6a13be2..fd4244023b33f 100644
--- a/drivers/iommu/io-pgfault.c
+++ b/drivers/iommu/io-pgfault.c
@@ -7,6 +7,7 @@
 
 #include <linux/iommu.h>
 #include <linux/list.h>
+#include <linux/sched/mm.h>
 #include <linux/slab.h>
 #include <linux/workqueue.h>
 
@@ -76,8 +77,57 @@ static int iopf_complete_group(struct device *dev, struct iopf_fault *iopf,
 static enum iommu_page_response_code
 iopf_handle_single(struct iopf_fault *iopf)
 {
-	/* TODO */
-	return -ENODEV;
+	vm_fault_t ret;
+	struct mm_struct *mm;
+	struct vm_area_struct *vma;
+	unsigned int access_flags = 0;
+	unsigned int fault_flags = FAULT_FLAG_REMOTE;
+	struct iommu_fault_page_request *prm = &iopf->fault.prm;
+	enum iommu_page_response_code status = IOMMU_PAGE_RESP_INVALID;
+
+	if (!(prm->flags & IOMMU_FAULT_PAGE_REQUEST_PASID_VALID))
+		return status;
+
+	mm = iommu_sva_find(prm->pasid);
+	if (IS_ERR_OR_NULL(mm))
+		return status;
+
+	down_read(&mm->mmap_sem);
+
+	vma = find_extend_vma(mm, prm->addr);
+	if (!vma)
+		/* Unmapped area */
+		goto out_put_mm;
+
+	if (prm->perm & IOMMU_FAULT_PERM_READ)
+		access_flags |= VM_READ;
+
+	if (prm->perm & IOMMU_FAULT_PERM_WRITE) {
+		access_flags |= VM_WRITE;
+		fault_flags |= FAULT_FLAG_WRITE;
+	}
+
+	if (prm->perm & IOMMU_FAULT_PERM_EXEC) {
+		access_flags |= VM_EXEC;
+		fault_flags |= FAULT_FLAG_INSTRUCTION;
+	}
+
+	if (!(prm->perm & IOMMU_FAULT_PERM_PRIV))
+		fault_flags |= FAULT_FLAG_USER;
+
+	if (access_flags & ~vma->vm_flags)
+		/* Access fault */
+		goto out_put_mm;
+
+	ret = handle_mm_fault(vma, prm->addr, fault_flags);
+	status = ret & VM_FAULT_ERROR ? IOMMU_PAGE_RESP_INVALID :
+		IOMMU_PAGE_RESP_SUCCESS;
+
+out_put_mm:
+	up_read(&mm->mmap_sem);
+	mmput(mm);
+
+	return status;
 }
 
 static void iopf_handle_group(struct work_struct *work)
@@ -112,6 +162,29 @@ static void iopf_handle_group(struct work_struct *work)
  *
  * Add a fault to the device workqueue, to be handled by mm.
  *
+ * This module doesn't handle PCI PASID Stop Marker; IOMMU drivers must discard
+ * them before reporting faults. A PASID Stop Marker (LRW = 0b100) doesn't
+ * expect a response. It may be generated when disabling a PASID (issuing a
+ * PASID stop request) by some PCI devices.
+ *
+ * The PASID stop request is issued by the device driver before unbind(). Once
+ * it completes, no page request is generated for this PASID anymore and
+ * outstanding ones have been pushed to the IOMMU (as per PCIe 4.0r1.0 - 6.20.1
+ * and 10.4.1.2 - Managing PASID TLP Prefix Usage). Some PCI devices will wait
+ * for all outstanding page requests to come back with a response before
+ * completing the PASID stop request. Others do not wait for page responses, and
+ * instead issue this Stop Marker that tells us when the PASID can be
+ * reallocated.
+ *
+ * It is safe to discard the Stop Marker because it is an optimization.
+ * a. Page requests, which are posted requests, have been flushed to the IOMMU
+ *    when the stop request completes.
+ * b. We flush all fault queues on unbind() before freeing the PASID.
+ *
+ * So even though the Stop Marker might be issued by the device *after* the stop
+ * request completes, outstanding faults will have been dealt with by the time
+ * we free the PASID.
+ *
  * Return: 0 on success and <0 on error.
  */
 int iommu_queue_iopf(struct iommu_fault *fault, void *cookie)
-- 
2.26.0