x86: disable intel_iommu support by default

Due to recurring issues with DMAR support on certain platforms.
There's a number of filesystem corruption incidents reported:

  https://bugzilla.redhat.com/show_bug.cgi?id=479996
  http://bugzilla.kernel.org/show_bug.cgi?id=12578

Provide a Kconfig option to change whether it is enabled by
default.

If disabled, it can still be reenabled by passing intel_iommu=on to the
kernel. Keep the .config option off by default.

Signed-off-by: Kyle McMartin <kyle@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-By: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 11 insertions, 0 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 73f7fe8fd4d1..9c39095b33fc 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1802,6 +1802,17 @@ config DMAR
           and include PCI device scope covered by these DMA
           remapping devices.
 
+config DMAR_DEFAULT_ON
+        def_bool n
+        prompt "Enable DMA Remapping Devices by default"
+        depends on DMAR
+        help
+          Selecting this option will enable a DMAR device at boot time if
+          one is found. If this option is not selected, DMAR support can
+          be enabled by passing intel_iommu=on to the kernel. It is
+          recommended you say N here while the DMAR code remains
+          experimental.
+
 config DMAR_GFX_WA
         def_bool y
         prompt "Support for Graphics workaround"