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

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> 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


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