APPLIED[G]: [PATCH][SRU][F/aws, G/aws] UBUNTU: SAUCE: [aws] iommu: set the default iommu-dma mode as non-strict

[Ian May]

Applied to G/aws/master

Thanks,
Ian

On 2020-10-30 18:33:40 , Andrea Righi wrote:
> BugLink: https://bugs.launchpad.net/bugs/1902281
> 
> Relax the synchronous IOMMU TLB invalidation constraint by default to
> get a significant performance improvement on some AWS arm64 instance
> types.
> 
> This is a performance vs security tradeoff and it is not suitable for
> the generic kernel. In the particular AWS environment it is reasonable
> to relax the constraint without realisticly introducing security flaws.
> 
> Signed-off-by: Andrea Righi <andrea.righi at canonical.com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 4 ++--
>  drivers/iommu/iommu.c                           | 2 +-
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index fb3eade0b7c5..a27706cde3c7 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1835,13 +1835,13 @@
>  
>  	iommu.strict=	[ARM64] Configure TLB invalidation behaviour
>  			Format: { "0" | "1" }
> -			0 - Lazy mode.
> +			0 - Lazy mode (default).
>  			  Request that DMA unmap operations use deferred
>  			  invalidation of hardware TLBs, for increased
>  			  throughput at the cost of reduced device isolation.
>  			  Will fall back to strict mode if not supported by
>  			  the relevant IOMMU driver.
> -			1 - Strict mode (default).
> +			1 - Strict mode.
>  			  DMA unmap operations invalidate IOMMU hardware TLBs
>  			  synchronously.
>  
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 9d7232e26ecf..50851f4e90d2 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -28,7 +28,7 @@ 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;
>  static u32 iommu_cmd_line __read_mostly;
>  
>  struct iommu_group {
> -- 
> 2.27.0
> 
> 
> -- 
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