linux-kernel - Re: [PATCH v10 1/3] iommu: Enhance IOMMU default DMA mode build options

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Date:   Fri, 4 Jun 2021 10:54:30 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     John Garry <john.garry@...wei.com>, <joro@...tes.org>,
        <will@...nel.org>, <dwmw2@...radead.org>,
        <baolu.lu@...ux.intel.com>, <robin.murphy@....com>
CC:     <linux-kernel@...r.kernel.org>, <iommu@...ts.linux-foundation.org>,
        <linuxarm@...wei.com>, <chenxiang66@...ilicon.com>
Subject: Re: [PATCH v10 1/3] iommu: Enhance IOMMU default DMA mode build
 options



On 2021/6/3 21:58, John Garry wrote:
> From: Zhen Lei <thunder.leizhen@...wei.com>
> 
> First, add build options IOMMU_DEFAULT_{LAZY|STRICT}, so that we have the
> opportunity to set {lazy|strict} mode as default at build time. Then put
> the two config options in an choice, as they are mutually-exclusive.
> 
> [jpg: Make choice between strict and lazy only (and not passthrough)]
> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
> Signed-off-by: John Garry <john.garry@...wei.com>
> ---
>  drivers/iommu/Kconfig | 34 ++++++++++++++++++++++++++++++++++
>  drivers/iommu/iommu.c |  3 ++-
>  2 files changed, 36 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index 1f111b399bca..12ef90256df8 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -90,6 +90,40 @@ config IOMMU_DEFAULT_PASSTHROUGH
>  
>  	  If unsure, say N here.
>  
> +choice
> +	prompt "IOMMU default DMA mode"
> +	depends on IOMMU_API

config INTEL_IOMMU
        depends on PCI_MSI && ACPI && (X86 || IA64)

config AMD_IOMMU
        depends on X86_64 && PCI && ACPI && HAVE_CMPXCHG_DOUBLE

config ARM_SMMU_V3
        depends on ARM64

"depends on ARM_SMMU_V3 || INTEL_IOMMU || AMD_IOMMU" may need to be added, because it doesn't work on other platforms.

or "depends on X86 || IA64 || X86_64 || ARM64"

> +
> +	default IOMMU_DEFAULT_STRICT
> +	help
> +	  This option allows an IOMMU DMA mode to be chosen at build time, to
> +	  override the default DMA mode of each ARCH, removing the need to
> +	  pass in kernel parameters through command line. It is still possible
> +	  to provide ARCH-specific or common boot options to override this
> +	  option.
> +
> +	  If unsure, keep the default.
> +
> +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 slower in some
> +	  high performace scenarios.
> +
> +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 966426a96520..177b0dafc535 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -29,7 +29,8 @@ static struct kset *iommu_group_kset;
>  static DEFINE_IDA(iommu_group_ida);
>  
>  static unsigned int iommu_def_domain_type __read_mostly;
> -static bool iommu_dma_strict __read_mostly = true;
> +static bool iommu_dma_strict __read_mostly =
> +			IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);

Currently, a maximum of 100 columns are allowed in a row.

>  static u32 iommu_cmd_line __read_mostly;
>  
>  struct iommu_group {
>