Re: [Qemu-devel] [PATCH 2/3] exec: simplify address_space_get_iotlb_entry

[David Gibson <david@gibson.dropbear.id.au>]

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On Sun, Jun 11, 2017 at 01:09:26PM +0300, Michael S. Tsirkin wrote:
> On Fri, Jun 09, 2017 at 09:58:47AM +0800, Peter Xu wrote:
> > > > The problem is that when I was fixing the problem that vhost had with
> > > > PT (a764040, "exec: abstract address_space_do_translate()"), I did
> > > > broke the IOTLB translation a bit (it was using page masks). IMHO we
> > > > need to fix it first for correctness (patch 1/2).
> > > > 
> > > > For patch 3, if we can have Jason's patch to allow dynamic
> > > > iommu_platform switching, that'll be the best, then I can rewrite
> > > > patch 3 with the switching logic rather than caching anything. But
> > > > IMHO that can be separated from patch 1/2 if you like.
> > > > 
> > > > Or do you have better suggestion on how should we fix it?
> > > > 
> > > > Thanks,
> > > 
> > > Can we drop masks completely and replace with length? I think we
> > > should do that instead of trying to fix masks.
> > 
> > Do you mean to modify IOMMUTLBEntry.addr_mask into length?
> 
> I think it's better than alternatives.
> 
> > Again, I am not sure this is good... At least we need to get ack from
> > David since spapr should be the initial user of it, and possibly also
> > Alex since vfio should be assuming that (IIUC both in QEMU and kernel)
> > addr_mask is page masks rather than arbirary length.
> > 
> > (CC Alex)
> > 
> > Thanks,
> 
> Callbacks that need powers of two can easily split up the range.

I think I missed part of the thread.  What's the original use case for
non-power-of-two IOTLB entries?  It certainly won't happen on Power.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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