[PATCH v3 1/2] iommu: Add iommu_get_pci_resv_windows() helper

[Guanghui Feng <guanghuifeng@linux.alibaba.com>]

Add a common helper that walks a PCI device's host bridge MMIO windows
and returns them as IOMMU_RESV_RESERVED regions in a list.  This
provides a reusable interface for subsystems that need visibility into
PCI host bridge MMIO address ranges, such as iommufd which wants to
expose these ranges to userspace for opt-in IOVA avoidance.

The helper builds its results in a local list using
iommu_insert_resv_region() so entries are sorted by start address and
overlapping same-type regions are merged.  On allocation failure the
partial list is freed internally, leaving the caller's list head
unmodified.

Note: commit cd2c9fcf5c66 ("iommu/dma: Move PCI window region reservation back into dma specific path.")
intentionally keeps PCI window reservation out of the IOMMU group-level
reserved region API.  This helper respects that boundary: it does not
inject windows into iommu_get_group_resv_regions().  Consumers that need
this information call the helper directly.

Signed-off-by: Guanghui Feng <guanghuifeng@linux.alibaba.com>
---
 drivers/iommu/iommu-priv.h | 12 ++++++++
 drivers/iommu/iommu.c      | 57 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 69 insertions(+)

diff --git a/drivers/iommu/iommu-priv.h b/drivers/iommu/iommu-priv.h
index aaffad5854fc..17f2234dabd4 100644
--- a/drivers/iommu/iommu-priv.h
+++ b/drivers/iommu/iommu-priv.h
@@ -123,4 +123,16 @@ static inline void iommu_debug_init(void)
 
 #endif /* CONFIG_IOMMU_DEBUG_PAGEALLOC */
 
+struct pci_dev;
+
+#ifdef CONFIG_PCI
+int iommu_get_pci_resv_windows(struct pci_dev *dev, struct list_head *head);
+#else
+static inline int iommu_get_pci_resv_windows(struct pci_dev *dev,
+					     struct list_head *head)
+{
+	return 0;
+}
+#endif /* CONFIG_PCI */
+
 #endif /* __LINUX_IOMMU_PRIV_H */
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index cd1bca7ede9a..25bc99114e1e 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -945,6 +945,63 @@ iommu_insert_device_resv_regions(struct list_head *dev_resv_regions,
 	return ret;
 }
 
+#ifdef CONFIG_PCI
+/**
+ * iommu_get_pci_resv_windows - collect PCI host bridge MMIO windows as
+ *                               reserved regions
+ * @dev: PCI device whose host bridge to scan
+ * @head: list head to append iommu_resv_region entries to
+ *
+ * Walks the MMIO windows of @dev's PCI host bridge and inserts an
+ * IOMMU_RESV_RESERVED region for each one using iommu_insert_resv_region(),
+ * keeping the entries sorted by start address and merging overlapping
+ * regions of the same type.  On success the inserted entries are appended
+ * to @head and the caller must free them with kfree() when done.  On
+ * failure any entries built so far are freed internally and @head is left
+ * unmodified.
+ *
+ * Returns 0 on success, negative errno on failure.
+ */
+int iommu_get_pci_resv_windows(struct pci_dev *dev, struct list_head *head)
+{
+	struct pci_host_bridge *bridge = pci_find_host_bridge(dev->bus);
+	struct iommu_resv_region *region, *next;
+	struct resource_entry *window;
+	LIST_HEAD(resv_windows);
+	int ret;
+
+	if (!bridge)
+		return -ENODEV;
+
+	resource_list_for_each_entry(window, &bridge->windows) {
+		struct iommu_resv_region tmp = {
+			.type = IOMMU_RESV_RESERVED,
+		};
+
+		if (resource_type(window->res) != IORESOURCE_MEM)
+			continue;
+
+		tmp.start = window->res->start - window->offset;
+		tmp.length = window->res->end - window->res->start + 1;
+
+		ret = iommu_insert_resv_region(&tmp, &resv_windows);
+		if (ret)
+			goto err_free;
+	}
+
+	list_splice_tail(&resv_windows, head);
+	return 0;
+
+err_free:
+	list_for_each_entry_safe(region, next, &resv_windows, list) {
+		list_del(&region->list);
+		kfree(region);
+	}
+	return ret;
+}
+EXPORT_SYMBOL_GPL(iommu_get_pci_resv_windows);
+#endif /* CONFIG_PCI */
+
 int iommu_get_group_resv_regions(struct iommu_group *group,
 				 struct list_head *head)
 {
-- 
2.43.7