linux-kernel - Re: [PATCH] iommu/arm-smmu: Return IOVA in iova_to

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Message-ID: <20170424144429.GI12323@arm.com>
Date:   Mon, 24 Apr 2017 15:44:30 +0100
From:   Will Deacon <will.deacon@....com>
To:     sunil.kovvuri@...il.com
Cc:     iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        robert.richter@...ium.com, Sunil Goutham <sgoutham@...ium.com>
Subject: Re: [PATCH] iommu/arm-smmu: Return IOVA in iova_to_phys when SMMU is
 bypassed

On Mon, Apr 17, 2017 at 05:27:26PM +0530, sunil.kovvuri@...il.com wrote:
> From: Sunil Goutham <sgoutham@...ium.com>
> 
> For software initiated address translation, when domain type is
> IOMMU_DOMAIN_IDENTITY i.e SMMU is bypassed, mimic HW behavior
> i.e return the same IOVA as translated address.
> 
> This patch is an extension to Will Deacon's patchset 
> "Implement SMMU passthrough using the default domain".

Are you actually seeing an issue here? If so, why isn't SMMUv3 affected too?

> Signed-off-by: Sunil Goutham <sgoutham@...ium.com>
> ---
>  drivers/iommu/arm-smmu.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index 41afb07..2f4a130 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -1405,6 +1405,9 @@ static phys_addr_t arm_smmu_iova_to_phys(struct iommu_domain *domain,
>  	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
>  	struct io_pgtable_ops *ops= smmu_domain->pgtbl_ops;
>  
> +	if (domain->type == IOMMU_DOMAIN_IDENTITY)
> +		return iova;
> +
>  	if (!ops)
>  		return 0;

I'd have thought ops would be NULL, since arm_smmu_init_domain_context
doesn't allocate them for an identity domain.

I don't understand this patch. Please can you explain the problem more
clearly?

Will