From b637576aff3aad57c332710d84d34d445ca7f5dd Mon Sep 17 00:00:00 2001
From: tychon <tychon@FreeBSD.org>
Date: Wed, 27 Mar 2019 20:15:51 +0000
Subject: [PATCH] Use the BUS_DMA_NOWRITE flag to expose and create the
 read-only VT-d IOMMU mappings.

Reviewed by:	kib
Sponsored by:	Dell EMC Isilon
Differential Revision:	https://reviews.freebsd.org/D19729
---
 sys/x86/iommu/busdma_dmar.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/sys/x86/iommu/busdma_dmar.c b/sys/x86/iommu/busdma_dmar.c
index c4bcef01b461..a8d02a5af96d 100644
--- a/sys/x86/iommu/busdma_dmar.c
+++ b/sys/x86/iommu/busdma_dmar.c
@@ -527,7 +527,8 @@ dmar_bus_dmamap_load_something1(struct bus_dma_tag_dmar *tag,
 			gas_flags |= DMAR_GM_CANSPLIT;
 
 		error = dmar_gas_map(domain, &tag->common, size, offset,
-		    DMAR_MAP_ENTRY_READ | DMAR_MAP_ENTRY_WRITE,
+		    DMAR_MAP_ENTRY_READ |
+		    ((flags & BUS_DMA_NOWRITE) == 0 ? DMAR_MAP_ENTRY_WRITE : 0),
 		    gas_flags, ma + idx, &entry);
 		if (error != 0)
 			break;