Re: [Xen-devel] [PATCH 3/4] amd iommu: Large io page support - enablement

[Wei Wang2 <wei.wang2@xxxxxxx>]

On Friday 03 December 2010 17:24:53 Keir Fraser wrote:
> Well, let's see. The change to p2m_set_entry() now allows (superpage) calls
> to the iommu mapping functions even if !need_iommu(). That seems a semantic
> change. 
That is because we have iommu_populate_page_table() which will delay io page 
table construction until device assignment. But this function can only 
updates io page table with 4k entries. I didn't find a better way to tracking 
page orders after page allocation (Q: could we extend struct page_info to 
cache page orders?). So my thought is to update IO page table earlier. And 
therefore, enabling super io page will also disable lazy io page table 
construction.  

Also, without need_iommu() checking both passthru and non-passthru guests will 
get io page table allocation. Since super paging will highly reduce io page 
table size, we might not waste too much memories here...

> Also I don't want the superpage command-line parameter, but I see 
> why you added it, as you couldn't be bothered to fix up the Intel side to
> work properly, so you left in the onld p2m_set_entry() code for that case.
> That's unacceptable. Get rid of the command-line parameter, get rid of the
> new [un]map_pages iommu hooks and extend the existing map/unmap hooks
> instead, and naturally do that for the Intel side as well as the AMD side
> (of course, on the Intel side you can just do a dumb implementation of
> map_pages which just loops over the existing single-page-at-a-time code --
> you need to keep the Intel side working, but you don't have to do the work
> to make it faster than it is already).
Understood..It will be fixed.

> I'm going to stop reading this patch series now and wait for a better one.
Yes, a better one will be given soon..

Thanks,
Wei
>  -- Keir
>
> On 03/12/2010 08:03, "Wei Wang2" <wei.wang2@xxxxxxx> wrote:
> > Enable super iommu support on amd systems.
> > Thanks,
> > We
> > Signed-off-by: Wei Wang <wei.wang2@xxxxxxx>
> > --
> > Legal Information:
> > Advanced Micro Devices GmbH
> > Sitz: Dornach, Gemeinde Aschheim,
> > Landkreis München Registergericht München,
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> > Alberto Bozzo, Andrew Bowd
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