Re: [Xen-devel] Unshared IOMMU issues

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.02.17 at 16:02, <olekstysh@xxxxxxxxx> wrote:
> On Thu, Feb 16, 2017 at 11:36 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>>> On 15.02.17 at 18:43, <olekstysh@xxxxxxxxx> wrote:
>>> 1.
>>> I need:
>>> Allow P2M core on ARM to update IOMMU mapping from the first 
>>> "p2m_set_entry".
>>> I do:
>>> I explicitly set need_iommu flag for *every* guest domain during
>>> iommu_domain_init() on ARM in case if page table is not shared.
>>> At that moment I have no knowledge about will any device be assigned
>>> to this domain or not. I am just want to receive all mapping updates
>>> from P2M code. The P2M will update IOMMU mapping only when need_iommu
>>> is set and page table is not shared.
>>> I have doubts:
>>> Is it correct to just force need_iommu flag?
>>
>> No, I don't think so. This is a waste of a measurable amount of
>> resources when page tables aren't shared.
>>
>>> Or maybe another flag should be introduced?
>>
>> Not sure what you think of here. Where's the problem with building
>> IOMMU page tables at the time the first device gets assigned, just
>> like x86 does?
> OK, I have already had a look at  arch_iommu_populate_page_table() for x86.
> I don't know at the moment how this solution can help me.
> There are a least two points the prevent me from doing the similar thing.
> 1. For create IOMMU mapping I need both mfn and gfn. (+ flags).
> I am able to get mfn only. How can I find corresponding gfn?

As the x86 one shows, via mfn_to_gmfn(). If ARM doesn't have
this, perhaps it needs to gain it?

> 2. The d->page_list seems only contains domain RAM (not 100% sure).
> Where can I get other regions (mmios, etc)?

These necessarily are being tracked for the domain, so you need to
take them from wherever they're stored on ARM.

Jan


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