[PATCH 4.4 060/146] iommu/amd: Fix unity mapping initialization race

From: Greg Kroah-Hartman
Date: Mon Jul 25 2016 - 17:17:39 EST

4.4-stable review patch. If anyone has any objections, please let me know.


From: Joerg Roedel <jroedel@xxxxxxx>

commit 522e5cb76d0663c88f96b6a8301451c8efa37207 upstream.

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')
Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

drivers/iommu/amd_iommu_init.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)

--- a/drivers/iommu/amd_iommu_init.c
+++ b/drivers/iommu/amd_iommu_init.c
@@ -1363,13 +1363,23 @@ static int __init amd_iommu_init_pci(voi

+ /*
+ * 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();


- ret = amd_iommu_init_api();
if (!ret)