Re: [Xen-devel] [PATCH v3 16/24] xen/passthrough: Introduce iommu_construct

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.01.15 at 11:37, <julien.grall@xxxxxxxxxx> wrote:
> On 21/01/2015 10:23, Jan Beulich wrote:
>>>>> On 20.01.15 at 18:11, <julien.grall@xxxxxxxxxx> wrote:
>>> While this function is currently only used for DOM0, this will be used
>>> in a later patch for guest non-PCI passthrough.
>>
>> Okay, but you shouldn't break (or alter in [seemingly] benign ways) the
>> Dom0 case imo.
> 
> As iommu_hwdom_init is initialized correctly the IOMMU for DOM0, 
> iommu_construct is a no-op.
> 
> Would an if ( need_iommu(d) ) will be more clear? Maybe we an assert 
> (!is_hardware_domain(d)).

Just think this through properly: iommu_hwdom_init() may leave
Dom0's ->need_iommu at 0 or 1 (depending on iommu_dom0_strict).
And iommu_construct() specifically is a nop only when ->need_iommu
is positive (x86's arch_iommu_populate_page_table() sets it to a
negative value to indicate "being set up", and I wonder how ARM
gets away without doing so).

Jan


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