linux-kernel - Re: [PATCH v8 04/11] iommu: Add sva iommu

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Date:   Mon, 20 Jun 2022 08:34:50 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>
Cc:     baolu.lu@...ux.intel.com,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Robin Murphy <robin.murphy@....com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Vinod Koul <vkoul@...nel.org>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        Jason Gunthorpe <jgg@...dia.com>, Will Deacon <will@...nel.org>
Subject: Re: [PATCH v8 04/11] iommu: Add sva iommu_domain support

On 2022/6/17 15:43, Tian, Kevin wrote:
>> From: Baolu Lu
>> Sent: Friday, June 10, 2022 3:16 PM
>>>
>>>> +#define __IOMMU_DOMAIN_HOST_VA	(1U << 5)  /* Host CPU virtual
>> address */
>>>
>>> Do you mean general CPU VA? or Host CPU VA, I'm reading the latter as
>> 2nd
>>> stage?
>>
>> Host CPU VA. In the near future, we will add another flag _GUEST_VA, so
>> that the shared page table types are distiguished.
> 
> How does the kernel knows that an user page table translates guest VA?
> IMHO I don't think the kernel should care about it except managing
> all the aspects related to the user page table itself...

Okay.

> 
>>
>>>
>>>> +
>>>>    /*
>>>>     * This are the possible domain-types
>>>>     *
>>>> @@ -86,15 +89,24 @@ 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)
>>>
>>> Doesn't shared automatically mean CPU VA? Do we need another flag?
>>
>> Yes. Shared means CPU VA, but there're many types. Besides above two, we
>> also see the shared KVM/EPT.
>>
> 
> Will the two sharing scenarios share any common code? If not then
> having a separate flag bit is meaningless.

So far, I haven't seen the need for common code. I've ever thought about
the common notifier callback for page table entry update of SVA and KVM.
But there has been no feasible plan.

> 
> It might be more straightforward to be:
> 
> #define IOMMU_DOMAIN_SVA	__IOMMU_DOMAIN_SVA
> #define IOMMU_DOMAIN_KVM __IOMMU_DOMAIN_KVM
> #define IOMMU_DOMAIN_USER __IOMMU_DOMAIN_USER

I am okay with this and we can add some shared bits later if we need to
consolidate any code.

--
Best regards,
baolu