linux-kernel - Re: [PATCH v13 1/6] iommu: Deprecate Intel and AMD cmdline methods to enable strict mode

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Date:   Thu, 17 Jun 2021 20:01:58 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     John Garry <john.garry@...wei.com>, joro@...tes.org,
        will@...nel.org, dwmw2@...radead.org, baolu.lu@...ux.intel.com,
        corbet@....net
Cc:     linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linuxarm@...wei.com, thunder.leizhen@...wei.com,
        chenxiang66@...ilicon.com, linux-doc@...r.kernel.org
Subject: Re: [PATCH v13 1/6] iommu: Deprecate Intel and AMD cmdline methods to
 enable strict mode

On 2021-06-16 12:03, John Garry wrote:
> Now that the x86 drivers support iommu.strict, deprecate the custom
> methods.
> 
> Signed-off-by: John Garry <john.garry@...wei.com>
> ---
>   Documentation/admin-guide/kernel-parameters.txt | 5 +++--
>   drivers/iommu/amd/init.c                        | 4 +++-
>   drivers/iommu/intel/iommu.c                     | 1 +
>   3 files changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 30e9dd52464e..fcbb36d6eea7 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -290,7 +290,8 @@
>   	amd_iommu=	[HW,X86-64]
>   			Pass parameters to the AMD IOMMU driver in the system.
>   			Possible values are:
> -			fullflush - enable flushing of IO/TLB entries when
> +			fullflush   [Deprecated, use iommu.strict instead]
> +				  - enable flushing of IO/TLB entries when
>   				    they are unmapped. Otherwise they are
>   				    flushed before they will be reused, which
>   				    is a lot of faster
> @@ -1947,7 +1948,7 @@
>   			bypassed by not enabling DMAR with this option. In
>   			this case, gfx device will use physical address for
>   			DMA.
> -		strict [Default Off]
> +		strict [Default Off] [Deprecated, use iommu.strict instead]
>   			With this option on every unmap_single operation will
>   			result in a hardware IOTLB flush operation as opposed
>   			to batching them for performance.

FWIW I'd be inclined to replace both whole descriptions with just 
something like "Deprecated, equivalent to iommu.strict=1".

> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index 46280e6e1535..9f3096d650aa 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -3098,8 +3098,10 @@ static int __init parse_amd_iommu_intr(char *str)
>   static int __init parse_amd_iommu_options(char *str)
>   {
>   	for (; *str; ++str) {
> -		if (strncmp(str, "fullflush", 9) == 0)
> +		if (strncmp(str, "fullflush", 9) == 0) {
> +			pr_warn("amd_iommu=fullflush deprecated; use iommu.strict instead\n");

Nit: maybe we should spell out "...use <option>=1 instead" in all of 
these messages just in case anyone takes them literally? (I'm not sure 
the options parse correctly with no argument)

Either way,

Acked-by: Robin Murphy <robin.murphy@....com>

Thanks,
Robin.

>   			amd_iommu_unmap_flush = true;
> +		}
>   		if (strncmp(str, "force_enable", 12) == 0)
>   			amd_iommu_force_enable = true;
>   		if (strncmp(str, "off", 3) == 0)
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index bd93c7ec879e..821d8227a4e6 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -454,6 +454,7 @@ static int __init intel_iommu_setup(char *str)
>   			pr_warn("intel_iommu=forcedac deprecated; use iommu.forcedac instead\n");
>   			iommu_dma_forcedac = true;
>   		} else if (!strncmp(str, "strict", 6)) {
> +			pr_warn("intel_iommu=strict deprecated; use iommu.strict instead\n");
>   			pr_info("Disable batched IOTLB flush\n");
>   			intel_iommu_strict = 1;
>   		} else if (!strncmp(str, "sp_off", 6)) {
>