linux-kernel - Re: [PATCH RFC 02/11] iommu: Add iommu

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Message-ID: <20220321114745.GI11336@nvidia.com>
Date:   Mon, 21 Mar 2022 08:47:45 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 02/11] iommu: Add iommu_domain type for SVA

On Sun, Mar 20, 2022 at 02:40:21PM +0800, Lu Baolu wrote:
> Add a new iommu domain type IOMMU_DOMAIN_SVA to represent an I/O page
> table which is shared from CPU host VA. Add a sva_cookie field in the
> iommu_domain structure to save the mm_struct which represent the CPU
> memory page table.
> 
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
>  include/linux/iommu.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 36f43af0af53..3e179b853380 100644
> +++ b/include/linux/iommu.h
> @@ -64,6 +64,9 @@ struct iommu_domain_geometry {
>  #define __IOMMU_DOMAIN_PT	(1U << 2)  /* Domain is identity mapped   */
>  #define __IOMMU_DOMAIN_DMA_FQ	(1U << 3)  /* DMA-API uses flush queue    */
>  
> +#define __IOMMU_DOMAIN_SHARED	(1U << 4)  /* Page table shared from CPU  */
> +#define __IOMMU_DOMAIN_HOST_VA	(1U << 5)  /* Host CPU virtual address */
> +
>  /*
>   * This are the possible domain-types
>   *
> @@ -86,6 +89,8 @@ struct iommu_domain_geometry {
>  #define IOMMU_DOMAIN_DMA_FQ	(__IOMMU_DOMAIN_PAGING |	\
>  				 __IOMMU_DOMAIN_DMA_API |	\
>  				 __IOMMU_DOMAIN_DMA_FQ)
> +#define IOMMU_DOMAIN_SVA	(__IOMMU_DOMAIN_SHARED |	\
> +				 __IOMMU_DOMAIN_HOST_VA)

Is there any use for this in the core code? I feel like flags should
only be created if the core code needs to test them in some way.

> @@ -95,6 +100,7 @@ struct iommu_domain {
>  	void *handler_token;
>  	struct iommu_domain_geometry geometry;
>  	struct iommu_dma_cookie *iova_cookie;
> +	struct mm_struct *sva_cookie;

Don't call a mm_struct a cookie please

And why do we need this in core code?

Jason