[PATCH v2 8/8] x86/iommu: make AMD-Vi and Intel VT-d support configurable

[Xenia Ragiadakou <burzalodowa@xxxxxxxxx>]

Provide the user with configuration control over the IOMMU support by making
AMD_IOMMU and INTEL_IOMMU options user selectable and able to be turned off.

However, there are cases where the IOMMU support is required, for instance for
a system with more than 254 CPUs. In order to prevent users from unknowingly
disabling it and ending up with a broken hypervisor, make the support user
selectable only if EXPERT is enabled.

To preserve the current default configuration of an x86 system, both options
depend on X86 and default to Y.

Signed-off-by: Xenia Ragiadakou <burzalodowa@xxxxxxxxx>
---

Changes in v2:
  - new patch that derives from patch 1/7 of v1 
  - replace --help-- with help
  - make the options visible if EXPERT is enabled
  - indicate the cases where the options need to be enabled

 xen/drivers/passthrough/Kconfig | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/xen/drivers/passthrough/Kconfig b/xen/drivers/passthrough/Kconfig
index 5c65567744..864fcf3b0c 100644
--- a/xen/drivers/passthrough/Kconfig
+++ b/xen/drivers/passthrough/Kconfig
@@ -38,10 +38,28 @@ config IPMMU_VMSA
 endif
 
 config AMD_IOMMU
-       def_bool y if X86
+       bool "AMD IOMMU" if EXPERT
+       depends on X86
+       default y
+       help
+         Enables I/O virtualization on platforms that implement the
+         AMD I/O Virtualization Technology (IOMMU).
+
+         If your system includes an IOMMU implementing AMD-Vi, say Y.
+         This is required if your system has more than 254 CPUs.
+         If in doubt, say Y.
 
 config INTEL_IOMMU
-       def_bool y if X86
+       bool "Intel VT-d" if EXPERT
+       depends on X86
+       default y
+       help
+         Enables I/O virtualization on platforms that implement the
+         Intel Virtualization Technology for Directed I/O (Intel VT-d).
+
+         If your system includes an IOMMU implementing Intel VT-d, say Y.
+         This is required if your system has more than 254 CPUs.
+         If in doubt, say Y.
 
 config IOMMU_FORCE_PT_SHARE
        bool
-- 
2.37.2