iommu/amd: Fix unity mapping initialization race

There is a race condition in the AMD IOMMU init code that
causes requested unity mappings to be blocked by the IOMMU
for a short period of time. This results on boot failures
and IO_PAGE_FAULTs on some machines.

Fix this by making sure the unity mappings are installed
before all other DMA is blocked.

Fixes: aafd8ba0ca74 ('iommu/amd: Implement add_device and remove_device')
Cc: stable@vger.kernel.org # v4.2+
Signed-off-by: Joerg Roedel <jroedel@suse.de>

1 files changed, 12 insertions, 2 deletions

diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
index d091defc3426..59741ead7e15 100644
--- a/drivers/iommu/amd_iommu_init.c
+++ b/drivers/iommu/amd_iommu_init.c
@@ -1568,13 +1568,23 @@ static int __init amd_iommu_init_pci(void)
                         break;
         }
 
+        /*
+         * Order is important here to make sure any unity map requirements are
+         * fulfilled. The unity mappings are created and written to the device
+         * table during the amd_iommu_init_api() call.
+         *
+         * After that we call init_device_table_dma() to make sure any
+         * uninitialized DTE will block DMA, and in the end we flush the caches
+         * of all IOMMUs to make sure the changes to the device table are
+         * active.
+         */
+        ret = amd_iommu_init_api();
+
         init_device_table_dma();
 
         for_each_iommu(iommu)
                 iommu_flush_all_caches(iommu);
 
-        ret = amd_iommu_init_api();
-
         if (!ret)
                 print_iommu_info();