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

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Message-ID: <645bd526-4eb0-4a36-2dda-023f009247ab@huawei.com>
Date:   Thu, 30 May 2019 13:20:16 +0100
From:   John Garry <john.garry@...wei.com>
To:     Zhen Lei <thunder.leizhen@...wei.com>,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        Robin Murphy <robin.murphy@....com>,
        "Will Deacon" <will.deacon@....com>,
        Joerg Roedel <joro@...tes.org>,
        Jonathan Corbet <corbet@....net>,
        linux-doc <linux-doc@...r.kernel.org>,
        Sebastian Ott <sebott@...ux.ibm.com>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>,
        "Martin Schwidefsky" <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        "Michael Ellerman" <mpe@...erman.id.au>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        David Woodhouse <dwmw2@...radead.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        x86 <x86@...nel.org>, linux-ia64 <linux-ia64@...r.kernel.org>
CC:     Hanjun Guo <guohanjun@...wei.com>, Linuxarm <linuxarm@...wei.com>
Subject: Re: [PATCH v8 1/7] iommu: enhance IOMMU default DMA mode build
 options

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@...wei.com>

> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.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;
>