[RFC PATCH v2 3/6] vfio: Add a page fault handler

[Shenming Lu]

VFIO manages the DMA mapping itself. To support IOPF for VFIO
devices, we add a VFIO page fault handler to serve the reported
page faults from the IOMMU driver. Besides, we can pre-map more
pages than requested at once to optimize for fewer page fault
handlings.

Signed-off-by: Shenming Lu <lushenming@xxxxxxxxxx>
---
 drivers/vfio/vfio.c             |  35 +++++++
 drivers/vfio/vfio_iommu_type1.c | 167 ++++++++++++++++++++++++++++++++
 include/linux/vfio.h            |   5 +
 3 files changed, 207 insertions(+)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 38779e6fd80c..77b29bbd3027 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -2354,6 +2354,41 @@ struct iommu_domain *vfio_group_iommu_domain(struct vfio_group *group)
 }
 EXPORT_SYMBOL_GPL(vfio_group_iommu_domain);
 
+int vfio_iommu_dev_fault_handler(struct iommu_fault *fault, void *data)
+{
+	struct device *dev = (struct device *)data;
+	struct vfio_container *container;
+	struct vfio_group *group;
+	struct vfio_iommu_driver *driver;
+	int ret;
+
+	if (!dev)
+		return -EINVAL;
+
+	group = vfio_group_get_from_dev(dev);
+	if (!group)
+		return -ENODEV;
+
+	ret = vfio_group_add_container_user(group);
+	if (ret)
+		goto out;
+
+	container = group->container;
+	driver = container->iommu_driver;
+	if (likely(driver && driver->ops->dma_map_iopf))
+		ret = driver->ops->dma_map_iopf(container->iommu_data,
+						fault, dev);
+	else
+		ret = -ENOTTY;
+
+	vfio_group_try_dissolve_container(group);
+
+out:
+	vfio_group_put(group);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(vfio_iommu_dev_fault_handler);
+
 /**
  * Module/class support
  */
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 03ccc11057af..167d52c1468b 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -3330,6 +3330,172 @@ static void vfio_iommu_type1_notify(void *iommu_data,
 	wake_up_all(&iommu->vaddr_wait);
 }
 
+/*
+ * To optimize for fewer page fault handlings, try to
+ * pre-map more pages than requested.
+ */
+#define IOPF_PREMAP_LEN		512
+
+static void unpin_pages_iopf(struct vfio_dma *dma,
+			     unsigned long pfn, unsigned long npages)
+{
+	while (npages--)
+		put_pfn(pfn++, dma->prot);
+}
+
+/*
+ * Return 0 on success or a negative error code, the
+ * number of pages contiguously pinned is in @*pinned.
+ */
+static int pin_pages_iopf(struct vfio_dma *dma, unsigned long vaddr,
+			  unsigned long npages, unsigned long *pfn_base,
+			  unsigned long *pinned, struct vfio_batch *batch)
+{
+	struct mm_struct *mm;
+	unsigned long pfn;
+	int ret = 0;
+	*pinned = 0;
+
+	mm = get_task_mm(dma->task);
+	if (!mm)
+		return -ENODEV;
+
+	if (batch->size) {
+		*pfn_base = page_to_pfn(batch->pages[batch->offset]);
+		pfn = *pfn_base;
+	} else
+		*pfn_base = 0;
+
+	while (npages) {
+		if (!batch->size) {
+			unsigned long req_pages = min_t(unsigned long, npages,
+							batch->capacity);
+
+			ret = vaddr_get_pfns(mm, vaddr, req_pages, dma->prot,
+					     &pfn, batch->pages);
+			if (ret < 0)
+				goto out;
+
+			batch->size = ret;
+			batch->offset = 0;
+			ret = 0;
+
+			if (!*pfn_base)
+				*pfn_base = pfn;
+		}
+
+		while (true) {
+			if (pfn != *pfn_base + *pinned)
+				goto out;
+
+			(*pinned)++;
+			npages--;
+			vaddr += PAGE_SIZE;
+			batch->offset++;
+			batch->size--;
+
+			if (!batch->size)
+				break;
+
+			pfn = page_to_pfn(batch->pages[batch->offset]);
+		}
+
+		if (unlikely(disable_hugepages))
+			break;
+	}
+
+out:
+	mmput(mm);
+	return ret;
+}
+
+static int vfio_iommu_type1_dma_map_iopf(void *iommu_data,
+					 struct iommu_fault *fault,
+					 struct device *dev)
+{
+	struct vfio_iommu *iommu = iommu_data;
+	dma_addr_t iova = ALIGN_DOWN(fault->prm.addr, PAGE_SIZE);
+	struct vfio_dma *dma;
+	int access_flags = 0;
+	size_t premap_len, map_len, mapped_len = 0;
+	unsigned long bit_offset, npages, i, vaddr, pfn;
+	struct vfio_batch batch;
+	enum iommu_page_response_code status = IOMMU_PAGE_RESP_INVALID;
+	struct iommu_page_response resp = {0};
+
+	mutex_lock(&iommu->lock);
+
+	dma = vfio_find_dma(iommu, iova, PAGE_SIZE);
+	if (!dma)
+		goto out_invalid;
+
+	if (fault->prm.perm & IOMMU_FAULT_PERM_READ)
+		access_flags |= IOMMU_READ;
+	if (fault->prm.perm & IOMMU_FAULT_PERM_WRITE)
+		access_flags |= IOMMU_WRITE;
+	if ((dma->prot & access_flags) != access_flags)
+		goto out_invalid;
+
+	bit_offset = (iova - dma->iova) >> PAGE_SHIFT;
+	if (IOPF_MAPPED_BITMAP_GET(dma, bit_offset))
+		goto out_success;
+
+	premap_len = IOPF_PREMAP_LEN << PAGE_SHIFT;
+	npages = dma->size >> PAGE_SHIFT;
+	map_len = PAGE_SIZE;
+	for (i = bit_offset + 1; i < npages; i++) {
+		if (map_len >= premap_len || IOPF_MAPPED_BITMAP_GET(dma, i))
+			break;
+		map_len += PAGE_SIZE;
+	}
+	vaddr = iova - dma->iova + dma->vaddr;
+	vfio_batch_init(&batch);
+
+	while (map_len) {
+		int ret;
+
+		ret = pin_pages_iopf(dma, vaddr + mapped_len,
+				     map_len >> PAGE_SHIFT, &pfn,
+				     &npages, &batch);
+		if (!npages)
+			break;
+
+		if (vfio_iommu_map(iommu, iova + mapped_len, pfn,
+				   npages, dma->prot)) {
+			unpin_pages_iopf(dma, pfn, npages);
+			vfio_batch_unpin(&batch, dma);
+			break;
+		}
+
+		bitmap_set(dma->iopf_mapped_bitmap,
+			   bit_offset + (mapped_len >> PAGE_SHIFT), npages);
+
+		unpin_pages_iopf(dma, pfn, npages);
+
+		map_len -= npages << PAGE_SHIFT;
+		mapped_len += npages << PAGE_SHIFT;
+
+		if (ret)
+			break;
+	}
+
+	vfio_batch_fini(&batch);
+
+	if (!mapped_len)
+		goto out_invalid;
+
+out_success:
+	status = IOMMU_PAGE_RESP_SUCCESS;
+
+out_invalid:
+	mutex_unlock(&iommu->lock);
+	resp.version		= IOMMU_PAGE_RESP_VERSION_1;
+	resp.grpid		= fault->prm.grpid;
+	resp.code		= status;
+	iommu_page_response(dev, &resp);
+	return 0;
+}
+
 static const struct vfio_iommu_driver_ops vfio_iommu_driver_ops_type1 = {
 	.name			= "vfio-iommu-type1",
 	.owner			= THIS_MODULE,
@@ -3345,6 +3511,7 @@ static const struct vfio_iommu_driver_ops vfio_iommu_driver_ops_type1 = {
 	.dma_rw			= vfio_iommu_type1_dma_rw,
 	.group_iommu_domain	= vfio_iommu_type1_group_iommu_domain,
 	.notify			= vfio_iommu_type1_notify,
+	.dma_map_iopf		= vfio_iommu_type1_dma_map_iopf,
 };
 
 static int __init vfio_iommu_type1_init(void)
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index b7e18bde5aa8..73af317a4343 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -99,6 +99,9 @@ struct vfio_iommu_driver_ops {
 						   struct iommu_group *group);
 	void		(*notify)(void *iommu_data,
 				  enum vfio_iommu_notify_type event);
+	int		(*dma_map_iopf)(void *iommu_data,
+					struct iommu_fault *fault,
+					struct device *dev);
 };
 
 extern int vfio_register_iommu_driver(const struct vfio_iommu_driver_ops *ops);
@@ -160,6 +163,8 @@ extern int vfio_unregister_notifier(struct device *dev,
 struct kvm;
 extern void vfio_group_set_kvm(struct vfio_group *group, struct kvm *kvm);
 
+extern int vfio_iommu_dev_fault_handler(struct iommu_fault *fault, void *data);
+
 /*
  * Sub-module helpers
  */
-- 
2.19.1