Re: [PATCH v8 04/11] iommu: Add sva iommu_domain support

[Baolu Lu <baolu.lu@linux.intel.com>]

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