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>

diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
index d091def..59741ea 100644 (file)
--- 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();