Re: [Xen-devel] [PATCH 2/4 v2] x86/EPT: refine direct MMIO checking when determining EMT

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Monday, April 28, 2014 4:25 PM
> 
> >>> On 28.04.14 at 09:59, <kevin.tian@xxxxxxxxx> wrote:
> >>  From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> >> @@ -810,10 +811,7 @@ int epte_get_entry_emt(struct domain *d,
> >>          return -1;
> >>      }
> >>
> >> -    if ( !iommu_enabled ||
> >> -         (rangeset_is_empty(d->iomem_caps) &&
> >> -          rangeset_is_empty(d->arch.ioport_caps) &&
> >> -          !has_arch_pdevs(d)) )
> >> +    if ( !need_iommu(d) && !cache_flush_permitted(d) )
> >
> > &&->||
> 
> No, specifically not - we shouldn't force WB in either case.
> 

well, I gave original comments with the impression that it's a cleanup patch
instead of fixing anything, e.g. iommu_enabled->need_iommu, and open-coding
to cache_flush_permitted. Based on that thought, && changes original meaning.

so you actually fix the conditions here. I didn't follow up latest advance in 
device
assignment recently. Could you elaborate in which situation I/O resources are
assigned while iommu is not required?

Thanks
Kevin

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