Re: [PATCH v8 1/7] iommu: enhance IOMMU default DMA mode build options

John Garry
2019-05-30T12:20:16Z

On 30/05/2019 04:48, 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.
>

Since this was not picked up, but modulo (somtimes same) comments below:

Reviewed-by: John Garry <john.garry@huawei.com>

> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
> ---
> drivers/iommu/Kconfig | 42 +++++++++++++++++++++++++++++++++++-------
> drivers/iommu/iommu.c | 3 ++-
> 2 files changed, 37 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index 83664db5221df02..d6a1a45f80ffbf5 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -75,17 +75,45 @@ 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 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_STRICT
> + help
> + This option allows IOMMU DMA mode to be chose at build time, to

As before:
/s/chose/chosen/, /s/allows IOMMU/allows an IOMMU/

> + override the default DMA mode of each ARCHs, removing the need to

Again, as before:
ARCHs should be singular

> + 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
> + translation. 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.

why no advisory on how to set if unsure?

> +
> +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 slower in some
> + high performace scenarios.

and here?

> +
> +endchoice
> +
> config OF_IOMMU
> def_bool y
> depends on OF && IOMMU_API
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 67ee6623f9b2a4d..56bce221285b15f 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_group {
> struct kobject kobj;
>