> -----Original Message-----
> From: Jan Beulich [mailto:[email protected]]
> Sent: 03 December 2018 10:21
> To: Andrew Cooper <[email protected]>; Paul Durrant
> <[email protected]>
> Cc: Brian Woods <[email protected]>; Suravee Suthikulpanit
> <[email protected]>; Julien Grall <[email protected]>;
> Roger Pau Monne <[email protected]>; Wei Liu <[email protected]>;
> Kevin Tian <[email protected]>; Stefano Stabellini
> <[email protected]>; xen-devel <[email protected]>
> Subject: Re: [PATCH 2/2] iommu: elide flushing for higher order map/unmap
> operations
>
> >>> On 30.11.18 at 13:49, <[email protected]> wrote:
> > On 30/11/2018 10:45, Paul Durrant wrote:
> >> +enum iommu_flush_type
> >> +{
> >> + IOMMU_FLUSH_none, /* no flush required */
> >> + IOMMU_FLUSH_added, /* no modified entries, just additional entries
> */
> >
> > IOMMU_FLUSH_invalid ? I think it is more descriptive of the scenario in
> > which it is used.
>
> This reads in a pretty misleading way to me. IOMMU_FLUSH_new
> or IOMMU_FLUSH_new_ents perhaps? Otoh I was quite okay with
> the name Paul had chosen.
I'll stick with those then :-)
>
> >> @@ -177,7 +184,8 @@ struct iommu_ops {
> >> * other by the caller in order to have meaningful results.
> >> */
> >> int __must_check (*map_page)(struct domain *d, dfn_t dfn, mfn_t
> mfn,
> >> - unsigned int flags);
> >> + unsigned int flags,
> >> + enum iommu_flush_type *flush_type);
> >
> > Maintaining the flush type by pointer is quite awkward.
> >
> > How about folding a positive flush type in with negative errors? i.e.
> > map_page() becomes < 0 on error, 0 for success/no flush and >0 for
> > success/w flush.
> >
> > I think the result would be rather cleaner to read.
>
> It would, but mapping operations with higher orders may fail
> _and_ require flushing.
>
Agreed. I did not want to confuse the error semantics with the flush semantics.
There is no order at this level as yet but, when one is added, this separation
- as you say - will become important.
Paul
> Jan
>
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