Enable the tdx-host module to get VTBAR address for every IOMMU device.
The VTBAR address is for TDX Module to identify the IOMMU device and
setup its trusted configuraion.

Suggested-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Xu Yilun <yilun.xu@linux.intel.com>
---
 include/linux/dmar.h       |  2 ++
 drivers/iommu/intel/dmar.c | 16 ++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/include/linux/dmar.h b/include/linux/dmar.h
index 692b2b445761..cd8d9f440975 100644
--- a/include/linux/dmar.h
+++ b/include/linux/dmar.h
@@ -86,6 +86,8 @@ extern struct list_head dmar_drhd_units;
 				dmar_rcu_check())			\
 		if (i=drhd->iommu, 0) {} else 
 
+int do_for_each_drhd_unit(int (*fn)(struct dmar_drhd_unit *));
+
 static inline bool dmar_rcu_check(void)
 {
 	return rwsem_is_locked(&dmar_global_lock) ||
diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
index 4f9571eee1d4..eea9ba691f99 100644
--- a/drivers/iommu/intel/dmar.c
+++ b/drivers/iommu/intel/dmar.c
@@ -2452,3 +2452,19 @@ bool dmar_platform_optin(void)
 	return ret;
 }
 EXPORT_SYMBOL_GPL(dmar_platform_optin);
+
+int do_for_each_drhd_unit(int (*fn)(struct dmar_drhd_unit *))
+{
+	struct dmar_drhd_unit *drhd;
+	int ret;
+
+	guard(rwsem_read)(&dmar_global_lock);
+
+	for_each_drhd_unit(drhd) {
+		ret = fn(drhd);
+		if (ret)
+			return ret;
+	}
+	return 0;
+}
+EXPORT_SYMBOL_GPL(do_for_each_drhd_unit);
-- 
2.25.1