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Subject[PATCH] iommu: Add config option to set passthrough as default
Date
This allows the default behavior to be controlled by a kernel config
option instead of changing the commandline for the kernel to include
"iommu.passthrough=on" or "iommu=pt" on machines where this is desired.

Likewise, for machines where this config option is enabled, it can be
disabled at boot time with "iommu.passthrough=off" or "iommu=nopt".

Also corrected iommu=pt documentation for IA-64, since it has no code that
parses iommu= at all.

Signed-off-by: Olof Johansson <olof@lixom.net>
---

Chances since v1:
- Added analogous behavior for Intel/AMD
- Added iommu=nopt for x86 and updated docs

Documentation/admin-guide/kernel-parameters.txt | 3 ++-
arch/x86/kernel/pci-dma.c | 8 ++++++++
drivers/iommu/Kconfig | 11 +++++++++++
drivers/iommu/iommu.c | 4 ++++
4 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index c9dbdf1009f1..4c822aa50f13 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1744,7 +1744,8 @@
merge
nomerge
soft
- pt [x86, IA-64]
+ pt [x86]
+ nopt [x86]
nobypass [PPC/POWERNV]
Disable IOMMU bypass, using IOMMU for PCI devices.

diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index ab5d9dd668d2..0acb135de7fb 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -40,8 +40,14 @@ int iommu_detected __read_mostly = 0;
* devices and allow every device to access to whole physical memory. This is
* useful if a user wants to use an IOMMU only for KVM device assignment to
* guests and not for driver dma translation.
+ * It is also possible to disable by default in kernel config, and enable with
+ * iommu=nopt at boot time.
*/
+#ifdef CONFIG_IOMMU_DEFAULT_PASSTHROUGH
+int iommu_pass_through __read_mostly = 1;
+#else
int iommu_pass_through __read_mostly;
+#endif

extern struct iommu_table_entry __iommu_table[], __iommu_table_end[];

@@ -135,6 +141,8 @@ static __init int iommu_setup(char *p)
#endif
if (!strncmp(p, "pt", 2))
iommu_pass_through = 1;
+ if (!strncmp(p, "nopt", 4))
+ iommu_pass_through = 0;

gart_parse_options(p);

diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index 568ae81b0e99..1813319c8342 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -70,6 +70,17 @@ config IOMMU_DEBUGFS
debug/iommu directory, and then populate a subdirectory with
entries as required.

+config IOMMU_DEFAULT_PASSTHROUGH
+ bool "IOMMU passthrough by default"
+ depends on IOMMU_API
+ help
+ Enable passthrough by default, removing the need to pass in
+ iommu.passthrough=on or iommu=pt through command line. If this
+ is enabled, you can still disable with iommu.passthrough=off
+ or iommu=nopt depending on the architecture.
+
+ If unsure, say N here.
+
config IOMMU_IOVA
tristate

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index d227b864a109..6f8f59684def 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -36,7 +36,11 @@

static struct kset *iommu_group_kset;
static DEFINE_IDA(iommu_group_ida);
+#ifdef CONFIG_IOMMU_DEFAULT_PASSTHROUGH
+static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_IDENTITY;
+#else
static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA;
+#endif

struct iommu_callback_data {
const struct iommu_ops *ops;
--
2.11.0
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