Re: [Xen-devel] [PATCH v3 2/3] svm: iommu: Only call guest_iommu_init() after initialized HVM domain

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 31.05.16 at 23:11, <suravee.suthikulpanit@xxxxxxx> wrote:
> On 5/26/2016 10:44 AM, Jan Beulich wrote:
>>>>> Suravee Suthikulanit <suravee.suthikulpanit@xxxxxxx> 05/25/16 9:01 PM >>>
>>> On 5/23/2016 6:54 AM, Jan Beulich wrote:
>>>>>>> On 22.05.16 at 01:42, <suravee.suthikulpanit@xxxxxxx> wrote:
>>>>> From: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
>>>>>
>>>>> The guest_iommu_init() is currently called by the following code path:
>>>>>
>>>>>     arch/x86/domain.c: arch_domain_create()
>>>>>       ]- drivers/passthrough/iommu.c: iommu_domain_init()
>>>>>         |- drivers/passthrough/amd/pci_amd_iommu.c: 
>>>>> amd_iommu_domain_init();
>>>>>           |- drivers/passthrough/amd/iommu_guest.c: guest_iommu_init()
>>>>>
>>>>> At this point, the hvm_domain_initialised() has not been called.
>>>>> So register_mmio_handler() in guest_iommu_init() silently fails.
>>>>> This patch moves the iommu_domain_init() to a later point after the
>>>>> hvm_domain_intialise() instead.
>>>>
>>>> That's one possible approach, which I continue to be not really
>>>> happy with. guest_iommu_init() really is HVM-specific, so maybe
>>>> no longer calling it from amd_iommu_domain_init() would be the
>>>> better solution (instead calling it from hvm_domain_initialise()
>>>> would then seem to be the better option). Thoughts?
>>>
>>> Then, this goes back to the approach I proposed in the v1 of this patch
>>> series, where I call guest_iommu_init/destroy() in the
>>> svm_domain_initialise/destroy().
>>>
>>> However, I'm still not quite clear in why the iommu_domain_init() is
>>> needed before hvm_domain_initialise().
>>
>> I think the two things are only lightly related. Changing the order of calls 
> is
>> generally fine, but recognizing that guest_iommu_init() really would better 
> be
>> called elsewhere makes that re-ordering simply unnecessary.
>>
>> Jan
> 
> So, let discussing these two things separately. I would propose to:
> 
> 1. Let's just remove the guest_iommu_init() for now since it's not 
> functioning, and it seems to not being called at a proper place 
> according to Jan. We will revisit this when we re-introduce and fully 
> test out the feature.

Fine with me.

> 2. As for the ordering of the iommu_domain_init() and hvm_domain_init() 
> , let's continue to discuss to find proper ordering if it needs changing.

Sure. The only thing I'd like to avoid is a change for the change's sake.

Jan


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