Re: [Xen-devel] [PATCH v12 8/9] mm / iommu: include need_iommu() test in iommu_use_hap_pt()

[Julien Grall <julien.grall@xxxxxxx>]

Hi Paul,

On 10/01/2018 11:51 AM, Paul Durrant wrote:
> > -----Original Message-----
> > From: Julien Grall [mailto:julien.grall@xxxxxxx]
> > Sent: 01 October 2018 11:37
> > To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
> > Cc: Jun Nakajima <jun.nakajima@xxxxxxxxx>; George Dunlap
> > <George.Dunlap@xxxxxxxxxx>; Jan Beulich <jbeulich@xxxxxxxx>; Andrew Cooper
> > <Andrew.Cooper3@xxxxxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > Subject: Re: [PATCH v12 8/9] mm / iommu: include need_iommu() test in
> > iommu_use_hap_pt()
> >
> > Hi Paul,
> >
> > On 09/27/2018 03:33 PM, Paul Durrant 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.
> > Well, I think we assume that iommu_use_hap_pt() will only be called when
> > need_iommu(d) == 1.
> Yes.
>
> > At the end, you will still need to check
> > need_iommu(d) outside because iommu_use_hap_pt() may now return 0 for
> > domain without IOMMU or for domain not sharing p2m with the IOMMU.
> >
> > Do you expect an improvement in long-term?
> Yes. The ultimate goal is the patch to split up need_iommu() into separate 
> macros for 'domain has IOMMU pt' and 'domain needs explicit sync of IOMMU pt' 
> and this seems like a logical step. For 'need explicit sync of IOMMU pt' to 
> true then 'has IOMMU pt' clearly needs to be true, so I wanted the macro for 
> 'sharing IOMMU pt' to have the same predicate.
Make senses. It didn't occur to me that was in preparation of the next 
patch.
For the Arm bits:

Acked-by: Julien Grall <julien.grall@xxxxxxx>

Cheers,

--
Julien Grall

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