Re: [Qemu-devel] [PATCH RFC v3 11/14] intel_iommu: provide its own replay() callback

[Jason Wang]

On 2017年01月13日 11:06, Peter Xu wrote:
> The default replay() don't work for VT-d since vt-d will have a huge
> default memory region which covers address range 0-(2^64-1). This will
> normally bring a dead loop when guest starts.

I think it just takes too much time instead of dead loop?

> The solution is simple - we don't walk over all the regions. Instead, we
> jump over the regions when we found that the page directories are empty.
> It'll greatly reduce the time to walk the whole region.

Yes, the problem is memory_region_is_iommu_reply() not smart because:

- It doesn't understand large page
- try go over all possible iova

So I'm thinking to introduce something like iommu_ops->iova_iterate() which

1) accept an start iova and return the next exist map
2) understand large page
3) skip unmapped iova

> To achieve this, we provided a page walk helper to do that, invoking
> corresponding hook function when we found an page we are interested in.
> vtd_page_walk_level() is the core logic for the page walking. It's
> interface is designed to suite further use case, e.g., to invalidate a
> range of addresses.
>
> Signed-off-by: Peter Xu<address@hidden>

For intel iommu, since we intercept all map and unmap, a more tricky 
ieda is to we can record the mappings internally in something like a 
rbtree which could be iterated during replay. This saves possible guest 
io page table traversal, but drawback is it may not survive from OOM 
attacker.

Thanks