[PATCH v6 0/1] iommu: enhance IOMMU dma mode build options

[PATCH v6 0/1] iommu: enhance IOMMU dma mode build options

[Zhen Lei]

v5 --> v6:
1. give up adding boot option iommu.dma_mode

v4 --> v5:
As Hanjun and Thomas Gleixner's suggestion:
1. Keep the old ARCH specific boot options no change.
2. Keep build option CONFIG_IOMMU_DEFAULT_PASSTHROUGH no change.

v4:
As Robin Murphy's suggestion:
"It's also not necessarily obvious to the user how this interacts with
IOMMU_DEFAULT_PASSTHROUGH, so if we really do go down this route, maybe it
would be better to refactor the whole lot into a single selection of something
like IOMMU_DEFAULT_MODE anyway."

In this version, I tried to normalize the IOMMU dma mode boot options for all
ARCHs. When IOMMU is enabled, there are 3 dma modes: paasthrough(bypass),
lazy(mapping but defer the IOTLB invalidation), strict. But currently each
ARCHs defined their private boot options, different with each other. For
example, to enable/disable "passthrough", ARM64 use iommu.passthrough=1/0,
X86 use iommu=pt/nopt, PPC/POWERNV use iommu=nobypass.

Zhen Lei (1):
  iommu: enhance IOMMU dma mode build options

 arch/ia64/kernel/pci-dma.c                |  2 +-
 arch/powerpc/platforms/powernv/pci-ioda.c |  3 ++-
 arch/s390/pci/pci_dma.c                   |  2 +-
 arch/x86/kernel/pci-dma.c                 |  7 ++---
 drivers/iommu/Kconfig                     | 44 ++++++++++++++++++++++++++-----
 drivers/iommu/amd_iommu_init.c            |  3 ++-
 drivers/iommu/intel-iommu.c               |  2 +-
 drivers/iommu/iommu.c                     |  3 ++-
 8 files changed, 48 insertions(+), 18 deletions(-)

-- 
1.8.3

[PATCH v6 1/1] iommu: enhance IOMMU dma mode build options

[Zhen Lei]

First, add build option IOMMU_DEFAULT_{LAZY|STRICT}, so that we have the
opportunity to set {lazy|strict} mode as default at build time. Then put
the three config options in an choice, make people can only choose one of
the three at a time.

The default IOMMU dma modes on each ARCHs have no change.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
 arch/ia64/kernel/pci-dma.c                |  2 +-
 arch/powerpc/platforms/powernv/pci-ioda.c |  3 ++-
 arch/s390/pci/pci_dma.c                   |  2 +-
 arch/x86/kernel/pci-dma.c                 |  7 ++---
 drivers/iommu/Kconfig                     | 44 ++++++++++++++++++++++++++-----
 drivers/iommu/amd_iommu_init.c            |  3 ++-
 drivers/iommu/intel-iommu.c               |  2 +-
 drivers/iommu/iommu.c                     |  3 ++-
 8 files changed, 48 insertions(+), 18 deletions(-)

diff --git a/arch/ia64/kernel/pci-dma.c b/arch/ia64/kernel/pci-dma.c
index fe988c49f01ce6a..655511dbf3c3b34 100644
--- a/arch/ia64/kernel/pci-dma.c
+++ b/arch/ia64/kernel/pci-dma.c
@@ -22,7 +22,7 @@
 int force_iommu __read_mostly;
 #endif

-int iommu_pass_through;
+int iommu_pass_through = IS_ENABLED(CONFIG_IOMMU_DEFAULT_PASSTHROUGH);

 static int __init pci_iommu_init(void)
 {
diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
index 3ead4c237ed0ec9..383e082a9bb985c 100644
--- a/arch/powerpc/platforms/powernv/pci-ioda.c
+++ b/arch/powerpc/platforms/powernv/pci-ioda.c
@@ -85,7 +85,8 @@ void pe_level_printk(const struct pnv_ioda_pe *pe, const char *level,
 	va_end(args);
 }

-static bool pnv_iommu_bypass_disabled __read_mostly;
+static bool pnv_iommu_bypass_disabled __read_mostly =
+			!IS_ENABLED(CONFIG_IOMMU_DEFAULT_PASSTHROUGH);
 static bool pci_reset_phbs __read_mostly;

 static int __init iommu_setup(char *str)
diff --git a/arch/s390/pci/pci_dma.c b/arch/s390/pci/pci_dma.c
index 9e52d1527f71495..784ad1e0acecfb1 100644
--- a/arch/s390/pci/pci_dma.c
+++ b/arch/s390/pci/pci_dma.c
@@ -17,7 +17,7 @@

 static struct kmem_cache *dma_region_table_cache;
 static struct kmem_cache *dma_page_table_cache;
-static int s390_iommu_strict;
+static int s390_iommu_strict = IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);

 static int zpci_refresh_global(struct zpci_dev *zdev)
 {
diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index d460998ae828514..fb2bab42a0a3173 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -43,11 +43,8 @@
  * 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
+int iommu_pass_through __read_mostly =
+			IS_ENABLED(CONFIG_IOMMU_DEFAULT_PASSTHROUGH);

 extern struct iommu_table_entry __iommu_table[], __iommu_table_end[];

diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index 6f07f3b21816c64..8a1f1793cde76b4 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -74,17 +74,47 @@ config IOMMU_DEBUGFS
 	  debug/iommu directory, and then populate a subdirectory with
 	  entries as required.

-config IOMMU_DEFAULT_PASSTHROUGH
-	bool "IOMMU passthrough by default"
+choice
+	prompt "IOMMU dma mode"
 	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.
+	default IOMMU_DEFAULT_PASSTHROUGH if (PPC_POWERNV && PCI)
+	default IOMMU_DEFAULT_LAZY if (AMD_IOMMU || INTEL_IOMMU || S390_IOMMU)
+	default IOMMU_DEFAULT_STRICT
+	help
+	  This option allows IOMMU dma mode to be chose at build time, to
+	  override the default dma mode of each ARCHs, removing the need to
+	  pass in kernel parameters through command line. You can still use
+	  ARCHs specific boot options to override this option again.
+
+config IOMMU_DEFAULT_PASSTHROUGH
+	bool "passthrough"
+	help
+	  In this mode, the dma access through IOMMU without any addresses
+	  transformation. That means, the wrong or illegal dma access can not
+	  be caught, no error information will be reported.

 	  If unsure, say N here.

+config IOMMU_DEFAULT_LAZY
+	bool "lazy"
+	help
+	  Support lazy mode, where for every IOMMU DMA unmap operation, the
+	  flush operation of IOTLB and the free operation of IOVA are deferred.
+	  They are only guaranteed to be done before the related IOVA will be
+	  reused.
+
+config IOMMU_DEFAULT_STRICT
+	bool "strict"
+	help
+	  For every IOMMU DMA unmap operation, the flush operation of IOTLB and
+	  the free operation of IOVA are guaranteed to be done in the unmap
+	  function.
+
+	  This mode is safer than the two above, but it maybe slow in some high
+	  performace scenarios.
+
+endchoice
+
 config OF_IOMMU
        def_bool y
        depends on OF && IOMMU_API
diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
index ff40ba758cf365e..16c02b08adb4cb2 100644
--- a/drivers/iommu/amd_iommu_init.c
+++ b/drivers/iommu/amd_iommu_init.c
@@ -166,7 +166,8 @@ struct ivmd_header {
 					   to handle */
 LIST_HEAD(amd_iommu_unity_map);		/* a list of required unity mappings
 					   we find in ACPI */
-bool amd_iommu_unmap_flush;		/* if true, flush on every unmap */
+bool amd_iommu_unmap_flush = IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);
+					/* if true, flush on every unmap */

 LIST_HEAD(amd_iommu_list);		/* list of all AMD IOMMUs in the
 					   system */
diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 28cb713d728ceef..0c3cc716210f35a 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -362,7 +362,7 @@ static int domain_detach_iommu(struct dmar_domain *domain,

 static int dmar_map_gfx = 1;
 static int dmar_forcedac;
-static int intel_iommu_strict;
+static int intel_iommu_strict = IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);
 static int intel_iommu_superpage = 1;
 static int intel_iommu_sm;
 static int iommu_identity_mapping;
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 109de67d5d727c2..0ec5952ac60e2a3 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -43,7 +43,8 @@
 #else
 static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA;
 #endif
-static bool iommu_dma_strict __read_mostly = true;
+static bool iommu_dma_strict __read_mostly =
+			IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);

 struct iommu_callback_data {
 	const struct iommu_ops *ops;
--
1.8.3

Re: [PATCH v6 0/1] iommu: enhance IOMMU dma mode build options

[Leizhen (ThunderTown)]

Hi all,
  Can anybody review or comment?


On 2019/4/18 21:57, Zhen Lei wrote:
> v5 --> v6:
> 1. give up adding boot option iommu.dma_mode
> 
> v4 --> v5:
> As Hanjun and Thomas Gleixner's suggestion:
> 1. Keep the old ARCH specific boot options no change.
> 2. Keep build option CONFIG_IOMMU_DEFAULT_PASSTHROUGH no change.
> 
> v4:
> As Robin Murphy's suggestion:
> "It's also not necessarily obvious to the user how this interacts with
> IOMMU_DEFAULT_PASSTHROUGH, so if we really do go down this route, maybe it
> would be better to refactor the whole lot into a single selection of something
> like IOMMU_DEFAULT_MODE anyway."
> 
> In this version, I tried to normalize the IOMMU dma mode boot options for all
> ARCHs. When IOMMU is enabled, there are 3 dma modes: paasthrough(bypass),
> lazy(mapping but defer the IOTLB invalidation), strict. But currently each
> ARCHs defined their private boot options, different with each other. For
> example, to enable/disable "passthrough", ARM64 use iommu.passthrough=1/0,
> X86 use iommu=pt/nopt, PPC/POWERNV use iommu=nobypass.
> 
> Zhen Lei (1):
>   iommu: enhance IOMMU dma mode build options
> 
>  arch/ia64/kernel/pci-dma.c                |  2 +-
>  arch/powerpc/platforms/powernv/pci-ioda.c |  3 ++-
>  arch/s390/pci/pci_dma.c                   |  2 +-
>  arch/x86/kernel/pci-dma.c                 |  7 ++---
>  drivers/iommu/Kconfig                     | 44 ++++++++++++++++++++++++++-----
>  drivers/iommu/amd_iommu_init.c            |  3 ++-
>  drivers/iommu/intel-iommu.c               |  2 +-
>  drivers/iommu/iommu.c                     |  3 ++-
>  8 files changed, 48 insertions(+), 18 deletions(-)
> 

-- 
Thanks!
BestRegards

Re: [PATCH v6 1/1] iommu: enhance IOMMU dma mode build options

[John Garry]

On 18/04/2019 14:57, Zhen Lei wrote:
> First, add build option IOMMU_DEFAULT_{LAZY|STRICT}, so that we have the
> opportunity to set {lazy|strict} mode as default at build time. Then put
> the three config options in an choice, make people can only choose one of
> the three at a time.
>
> The default IOMMU dma modes on each ARCHs have no change.
>
> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
> ---
>  arch/ia64/kernel/pci-dma.c                |  2 +-
>  arch/powerpc/platforms/powernv/pci-ioda.c |  3 ++-
>  arch/s390/pci/pci_dma.c                   |  2 +-
>  arch/x86/kernel/pci-dma.c                 |  7 ++---
>  drivers/iommu/Kconfig                     | 44 ++++++++++++++++++++++++++-----
>  drivers/iommu/amd_iommu_init.c            |  3 ++-
>  drivers/iommu/intel-iommu.c               |  2 +-
>  drivers/iommu/iommu.c                     |  3 ++-
>  8 files changed, 48 insertions(+), 18 deletions(-)
>
> diff --git a/arch/ia64/kernel/pci-dma.c b/arch/ia64/kernel/pci-dma.c
> index fe988c49f01ce6a..655511dbf3c3b34 100644
> --- a/arch/ia64/kernel/pci-dma.c
> +++ b/arch/ia64/kernel/pci-dma.c
> @@ -22,7 +22,7 @@
>  int force_iommu __read_mostly;
>  #endif
>
> -int iommu_pass_through;
> +int iommu_pass_through = IS_ENABLED(CONFIG_IOMMU_DEFAULT_PASSTHROUGH);
>
>  static int __init pci_iommu_init(void)
>  {
> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
> index 3ead4c237ed0ec9..383e082a9bb985c 100644
> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> @@ -85,7 +85,8 @@ void pe_level_printk(const struct pnv_ioda_pe *pe, const char *level,
>  	va_end(args);
>  }
>
> -static bool pnv_iommu_bypass_disabled __read_mostly;
> +static bool pnv_iommu_bypass_disabled __read_mostly =
> +			!IS_ENABLED(CONFIG_IOMMU_DEFAULT_PASSTHROUGH);
>  static bool pci_reset_phbs __read_mostly;
>
>  static int __init iommu_setup(char *str)
> diff --git a/arch/s390/pci/pci_dma.c b/arch/s390/pci/pci_dma.c
> index 9e52d1527f71495..784ad1e0acecfb1 100644
> --- a/arch/s390/pci/pci_dma.c
> +++ b/arch/s390/pci/pci_dma.c
> @@ -17,7 +17,7 @@
>
>  static struct kmem_cache *dma_region_table_cache;
>  static struct kmem_cache *dma_page_table_cache;
> -static int s390_iommu_strict;
> +static int s390_iommu_strict = IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);
>
>  static int zpci_refresh_global(struct zpci_dev *zdev)
>  {
> diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
> index d460998ae828514..fb2bab42a0a3173 100644
> --- a/arch/x86/kernel/pci-dma.c
> +++ b/arch/x86/kernel/pci-dma.c
> @@ -43,11 +43,8 @@
>   * 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
> +int iommu_pass_through __read_mostly =
> +			IS_ENABLED(CONFIG_IOMMU_DEFAULT_PASSTHROUGH);
>
>  extern struct iommu_table_entry __iommu_table[], __iommu_table_end[];
>
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index 6f07f3b21816c64..8a1f1793cde76b4 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -74,17 +74,47 @@ config IOMMU_DEBUGFS
>  	  debug/iommu directory, and then populate a subdirectory with
>  	  entries as required.
>
> -config IOMMU_DEFAULT_PASSTHROUGH
> -	bool "IOMMU passthrough by default"
> +choice
> +	prompt "IOMMU dma mode"

/s/dma/DMA/

And how about add "default", as in "Default IOMMU DMA mode" or "IOMMU 
default DMA mode"?

>  	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.
> +	default IOMMU_DEFAULT_PASSTHROUGH if (PPC_POWERNV && PCI)
> +	default IOMMU_DEFAULT_LAZY if (AMD_IOMMU || INTEL_IOMMU || S390_IOMMU)
> +	default IOMMU_DEFAULT_STRICT
> +	help
> +	  This option allows IOMMU dma mode to be chose at build time, to

again, capitalize acronyms, i.e. /s/dma/DMA/ (more of these above and below)

> +	  override the default dma mode of each ARCHs, removing the need to
> +	  pass in kernel parameters through command line. You can still use
> +	  ARCHs specific boot options to override this option again.
> +
> +config IOMMU_DEFAULT_PASSTHROUGH

I think that it may need to be indented, along with the other choices

> +	bool "passthrough"
> +	help
> +	  In this mode, the dma access through IOMMU without any addresses
> +	  transformation. That means, the wrong or illegal dma access can not

transformation, or translation?

> +	  be caught, no error information will be reported.
>
>  	  If unsure, say N here.
>
> +config IOMMU_DEFAULT_LAZY
> +	bool "lazy"
> +	help
> +	  Support lazy mode, where for every IOMMU DMA unmap operation, the
> +	  flush operation of IOTLB and the free operation of IOVA are deferred.
> +	  They are only guaranteed to be done before the related IOVA will be
> +	  reused.
> +
> +config IOMMU_DEFAULT_STRICT
> +	bool "strict"
> +	help
> +	  For every IOMMU DMA unmap operation, the flush operation of IOTLB and
> +	  the free operation of IOVA are guaranteed to be done in the unmap
> +	  function.
> +
> +	  This mode is safer than the two above, but it maybe slow in some high

slow, or slower? And passthough is not safe, so anything is implicitly 
safer.

> +	  performace scenarios.
> +
> +endchoice
> +
>  config OF_IOMMU
>         def_bool y
>         depends on OF && IOMMU_API
> diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
> index ff40ba758cf365e..16c02b08adb4cb2 100644
> --- a/drivers/iommu/amd_iommu_init.c
> +++ b/drivers/iommu/amd_iommu_init.c
> @@ -166,7 +166,8 @@ struct ivmd_header {
>  					   to handle */
>  LIST_HEAD(amd_iommu_unity_map);		/* a list of required unity mappings
>  					   we find in ACPI */
> -bool amd_iommu_unmap_flush;		/* if true, flush on every unmap */
> +bool amd_iommu_unmap_flush = IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);
> +					/* if true, flush on every unmap */
>
>  LIST_HEAD(amd_iommu_list);		/* list of all AMD IOMMUs in the
>  					   system */
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 28cb713d728ceef..0c3cc716210f35a 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -362,7 +362,7 @@ static int domain_detach_iommu(struct dmar_domain *domain,
>
>  static int dmar_map_gfx = 1;
>  static int dmar_forcedac;
> -static int intel_iommu_strict;
> +static int intel_iommu_strict = IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);
>  static int intel_iommu_superpage = 1;
>  static int intel_iommu_sm;
>  static int iommu_identity_mapping;
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 109de67d5d727c2..0ec5952ac60e2a3 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -43,7 +43,8 @@
>  #else
>  static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA;
>  #endif
> -static bool iommu_dma_strict __read_mostly = true;
> +static bool iommu_dma_strict __read_mostly =
> +			IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);
>
>  struct iommu_callback_data {
>  	const struct iommu_ops *ops;
> --
> 1.8.3
>
>
>
> .
>

Re: [PATCH v6 1/1] iommu: enhance IOMMU dma mode build options

[Leizhen (ThunderTown)]

On 2019/5/8 17:42, John Garry wrote:
> On 18/04/2019 14:57, Zhen Lei wrote:
>> First, add build option IOMMU_DEFAULT_{LAZY|STRICT}, so that we have the
>> opportunity to set {lazy|strict} mode as default at build time. Then put
>> the three config options in an choice, make people can only choose one of
>> the three at a time.
>>
>> The default IOMMU dma modes on each ARCHs have no change.
>>
>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>> ---
>>  arch/ia64/kernel/pci-dma.c                |  2 +-
>>  arch/powerpc/platforms/powernv/pci-ioda.c |  3 ++-
>>  arch/s390/pci/pci_dma.c                   |  2 +-
>>  arch/x86/kernel/pci-dma.c                 |  7 ++---
>>  drivers/iommu/Kconfig                     | 44 ++++++++++++++++++++++++++-----
>>  drivers/iommu/amd_iommu_init.c            |  3 ++-
>>  drivers/iommu/intel-iommu.c               |  2 +-
>>  drivers/iommu/iommu.c                     |  3 ++-
>>  8 files changed, 48 insertions(+), 18 deletions(-)
>>
>> diff --git a/arch/ia64/kernel/pci-dma.c b/arch/ia64/kernel/pci-dma.c
>> index fe988c49f01ce6a..655511dbf3c3b34 100644
>> --- a/arch/ia64/kernel/pci-dma.c
>> +++ b/arch/ia64/kernel/pci-dma.c
>> @@ -22,7 +22,7 @@
>>  int force_iommu __read_mostly;
>>  #endif
>>
>> -int iommu_pass_through;
>> +int iommu_pass_through = IS_ENABLED(CONFIG_IOMMU_DEFAULT_PASSTHROUGH);
>>
>>  static int __init pci_iommu_init(void)
>>  {
>> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
>> index 3ead4c237ed0ec9..383e082a9bb985c 100644
>> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
>> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
>> @@ -85,7 +85,8 @@ void pe_level_printk(const struct pnv_ioda_pe *pe, const char *level,
>>      va_end(args);
>>  }
>>
>> -static bool pnv_iommu_bypass_disabled __read_mostly;
>> +static bool pnv_iommu_bypass_disabled __read_mostly =
>> +            !IS_ENABLED(CONFIG_IOMMU_DEFAULT_PASSTHROUGH);
>>  static bool pci_reset_phbs __read_mostly;
>>
>>  static int __init iommu_setup(char *str)
>> diff --git a/arch/s390/pci/pci_dma.c b/arch/s390/pci/pci_dma.c
>> index 9e52d1527f71495..784ad1e0acecfb1 100644
>> --- a/arch/s390/pci/pci_dma.c
>> +++ b/arch/s390/pci/pci_dma.c
>> @@ -17,7 +17,7 @@
>>
>>  static struct kmem_cache *dma_region_table_cache;
>>  static struct kmem_cache *dma_page_table_cache;
>> -static int s390_iommu_strict;
>> +static int s390_iommu_strict = IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);
>>
>>  static int zpci_refresh_global(struct zpci_dev *zdev)
>>  {
>> diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
>> index d460998ae828514..fb2bab42a0a3173 100644
>> --- a/arch/x86/kernel/pci-dma.c
>> +++ b/arch/x86/kernel/pci-dma.c
>> @@ -43,11 +43,8 @@
>>   * 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
>> +int iommu_pass_through __read_mostly =
>> +            IS_ENABLED(CONFIG_IOMMU_DEFAULT_PASSTHROUGH);
>>
>>  extern struct iommu_table_entry __iommu_table[], __iommu_table_end[];
>>
>> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
>> index 6f07f3b21816c64..8a1f1793cde76b4 100644
>> --- a/drivers/iommu/Kconfig
>> +++ b/drivers/iommu/Kconfig
>> @@ -74,17 +74,47 @@ config IOMMU_DEBUGFS
>>        debug/iommu directory, and then populate a subdirectory with
>>        entries as required.
>>
>> -config IOMMU_DEFAULT_PASSTHROUGH
>> -    bool "IOMMU passthrough by default"
>> +choice
>> +    prompt "IOMMU dma mode"
> 
> /s/dma/DMA/
OK

> 
> And how about add "default", as in "Default IOMMU DMA mode" or "IOMMU default DMA mode"?
Yes. I prefer "IOMMU default DMA mode".

> 
>>      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.
>> +    default IOMMU_DEFAULT_PASSTHROUGH if (PPC_POWERNV && PCI)
>> +    default IOMMU_DEFAULT_LAZY if (AMD_IOMMU || INTEL_IOMMU || S390_IOMMU)
>> +    default IOMMU_DEFAULT_STRICT
>> +    help
>> +      This option allows IOMMU dma mode to be chose at build time, to
> 
> again, capitalize acronyms, i.e. /s/dma/DMA/ (more of these above and below)
OK, I will check it all. Thanks.

> 
>> +      override the default dma mode of each ARCHs, removing the need to
>> +      pass in kernel parameters through command line. You can still use
>> +      ARCHs specific boot options to override this option again.
>> +
>> +config IOMMU_DEFAULT_PASSTHROUGH
> 
> I think that it may need to be indented, along with the other choices
There is no problem. I referred to mm/Kconfig.

> 
>> +    bool "passthrough"
>> +    help
>> +      In this mode, the dma access through IOMMU without any addresses
>> +      transformation. That means, the wrong or illegal dma access can not
> 
> transformation, or translation?
I copied from somewhere. OK, "translation" will be more clear.

> 
>> +      be caught, no error information will be reported.
>>
>>        If unsure, say N here.
>>
>> +config IOMMU_DEFAULT_LAZY
>> +    bool "lazy"
>> +    help
>> +      Support lazy mode, where for every IOMMU DMA unmap operation, the
>> +      flush operation of IOTLB and the free operation of IOVA are deferred.
>> +      They are only guaranteed to be done before the related IOVA will be
>> +      reused.
>> +
>> +config IOMMU_DEFAULT_STRICT
>> +    bool "strict"
>> +    help
>> +      For every IOMMU DMA unmap operation, the flush operation of IOTLB and
>> +      the free operation of IOVA are guaranteed to be done in the unmap
>> +      function.
>> +
>> +      This mode is safer than the two above, but it maybe slow in some high
> 
> slow, or slower? And passthough is not safe, so anything is implicitly safer.
OK. I will change it to "slower".

> 
>> +      performace scenarios.
>> +
>> +endchoice
>> +
>>  config OF_IOMMU
>>         def_bool y
>>         depends on OF && IOMMU_API
>> diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
>> index ff40ba758cf365e..16c02b08adb4cb2 100644
>> --- a/drivers/iommu/amd_iommu_init.c
>> +++ b/drivers/iommu/amd_iommu_init.c
>> @@ -166,7 +166,8 @@ struct ivmd_header {
>>                         to handle */
>>  LIST_HEAD(amd_iommu_unity_map);        /* a list of required unity mappings
>>                         we find in ACPI */
>> -bool amd_iommu_unmap_flush;        /* if true, flush on every unmap */
>> +bool amd_iommu_unmap_flush = IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);
>> +                    /* if true, flush on every unmap */
>>
>>  LIST_HEAD(amd_iommu_list);        /* list of all AMD IOMMUs in the
>>                         system */
>> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
>> index 28cb713d728ceef..0c3cc716210f35a 100644
>> --- a/drivers/iommu/intel-iommu.c
>> +++ b/drivers/iommu/intel-iommu.c
>> @@ -362,7 +362,7 @@ static int domain_detach_iommu(struct dmar_domain *domain,
>>
>>  static int dmar_map_gfx = 1;
>>  static int dmar_forcedac;
>> -static int intel_iommu_strict;
>> +static int intel_iommu_strict = IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);
>>  static int intel_iommu_superpage = 1;
>>  static int intel_iommu_sm;
>>  static int iommu_identity_mapping;
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index 109de67d5d727c2..0ec5952ac60e2a3 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -43,7 +43,8 @@
>>  #else
>>  static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA;
>>  #endif
>> -static bool iommu_dma_strict __read_mostly = true;
>> +static bool iommu_dma_strict __read_mostly =
>> +            IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);
>>
>>  struct iommu_callback_data {
>>      const struct iommu_ops *ops;
>> -- 
>> 1.8.3
>>
>>
>>
>> .
>>
> 
> 
> 
> .
> 

-- 
Thanks!
BestRegards