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

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Date:   Tue, 22 Mar 2022 08:54:03 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     baolu.lu@...ux.intel.com, 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 2022/3/21 19:47, Jason Gunthorpe wrote:
> 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.

flags are some attributes of the domain and the combination of multiple
flags forms a domain type.

> 
>> @@ -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

Sure.

> 
> And why do we need this in core code?

Need to connect an SVA domain with mm.

Best regards,
baolu