Re: [Xen-devel] [PATCH v6 09/14] mm / iommu: include need_iommu() test in iommu_use_hap_pt()

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

> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Tuesday, September 11, 2018 5:48 PM
> 
> >>> On 11.09.18 at 11:39, <Paul.Durrant@xxxxxxxxxx> wrote:
> >>  -----Original Message-----
> >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> >> Sent: 07 September 2018 12:20
> >> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> >> Cc: Julien Grall <julien.grall@xxxxxxx>; Andrew Cooper
> >> <Andrew.Cooper3@xxxxxxxxxx>; George Dunlap
> >> <George.Dunlap@xxxxxxxxxx>; Jun Nakajima <jun.nakajima@xxxxxxxxx>;
> >> Stefano Stabellini <sstabellini@xxxxxxxxxx>; xen-devel <xen-
> >> devel@xxxxxxxxxxxxxxxxxxxx>
> >> Subject: Re: [PATCH v6 09/14] mm / iommu: include need_iommu() test
> in
> >> iommu_use_hap_pt()
> >>
> >> >>> On 23.08.18 at 11:47, <paul.durrant@xxxxxxxxxx> wrote:
> >> > The name 'iommu_use_hap_pt' suggests that that P2M table is in use
> as
> >> the
> >> > domain's IOMMU pagetable which, prior to this patch, is not strictly
> true
> >> > since the macro did not test whether the domain actually has IOMMU
> >> > mappings.
> >>
> >> Hmm, I would never have implied "has IOMMU mappings" from this
> >> variable name. To me it has always been "use HAP page tables for
> >> IOMMU if an IOMMU is in use". The code change looks sane, but
> >> I'm not sure it is a clear improvement. Hence I wonder whether you
> >> have a need for this change in subsequent patches which goes
> >> beyond what you say above.
> >>
> >
> > I could take it out but it would mean a non-trivial rebase, and to me - if
> > true - the name sill implies the IOMMU is in use for the domain so I'd like
> to
> > keep the change.
> 
> Let's broaden the Cc list a little - perhaps we can get further opinions this
> way.
> 

the previous definition checks hap_enabled:

-#define iommu_use_hap_pt(d) (hap_enabled(d) && iommu_hap_pt_share)

if following Jan's way it should be "use HAP page tables for IOMMU if an 
IOMMU is in use and HAP is enabled", then hap_enabled should be moved
out too.

including iommu check in the macro looks more consistent.

Thanks
Kevin

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