Re: [PATCH 1/5] iommu: Add capability IOMMU_CAP_BYPASS

[Robin Murphy]

On 19/07/17 10:33, Anup Patel wrote:
> Some of the IOMMUs (such as ARM SMMU) are capable of bypassing
> transactions for which no IOMMU domain is configured.
> 
> This patch adds IOMMU_CAP_BYPASS which can be used by IOMMU
> drivers to advertise transation bypass capability of an IOMMU.

Whatever the intended semantics of this are, I can't help thinking it
would be better served by allowing callers to explicitly allocate their
own IOMMU_DOMAIN_IDENTITY domains. That would also be useful for the
problem we have with legacy virtio devices behind real IOMMUs.

Robin.

> Signed-off-by: Anup Patel <anup.patel@xxxxxxxxxxxx>
> ---
>  include/linux/iommu.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 2cb54ad..6bbb4cc 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -101,6 +101,10 @@ enum iommu_cap {
>  					   transactions */
>  	IOMMU_CAP_INTR_REMAP,		/* IOMMU supports interrupt isolation */
>  	IOMMU_CAP_NOEXEC,		/* IOMMU_NOEXEC flag */
> +	IOMMU_CAP_BYPASS,		/*
> +					 * IOMMU can bypass transactions for
> +					 * which domain is not configured
> +					 */
>  };
>  
>  /*
>