> -----Original Message-----
> From: Julien Grall <[email protected]>
> Sent: 05 September 2019 20:59
> To: Paul Durrant <[email protected]>; [email protected]
> Cc: Jan Beulich <[email protected]>; Ian Jackson <[email protected]>;
> Wei Liu <[email protected]>;
> Andrew Cooper <[email protected]>; George Dunlap
> <[email protected]>; Konrad Rzeszutek
> Wilk <[email protected]>; Stefano Stabellini <[email protected]>;
> Tim (Xen.org)
> <[email protected]>; Anthony Perard <[email protected]>; Christian Lindig
> <[email protected]>; David Scott <[email protected]>; Volodymyr
> Babchuk
> <[email protected]>; Roger Pau Monne <[email protected]>
> Subject: Re: [PATCH v8 6/6] introduce a 'passthrough' configuration option to
> xl.cfg...
>
> Hi,
>
> On 9/2/19 3:50 PM, Paul Durrant wrote:
> > @@ -263,9 +263,17 @@ struct domain_iommu {
> > DECLARE_BITMAP(features, IOMMU_FEAT_count);
> >
> > /*
> > - * Does the guest reqire mappings to be synchonized, to maintain
> > - * the default dfn == pfn map. (See comment on dfn at the top of
> > - * include/xen/mm.h).
> > + * Does the guest share HAP mapping with the IOMMU? This is always
> > + * true for ARM systems and may be true for x86 systems where the
> > + * the hardware is capable.
> > + */
>
> I am worried that such comment may rot over the time. For instance, if
> we either add a new architecture or decide to stop sharing PT on Arm.
>
> I vaguely recall some potential issues with the MSI doorbells that would
> require us to unshare the PT when they will be supported in guest.
>
> I would suggest to either refers to the implementation of
> iommu_use_hap_pt() or drop completely the second sentence.
Ok, I'll just drop the sentence.
Paul
>
> > + bool hap_pt_share;
> > +
> > + /*
> > + * Does the guest require mappings to be synchronized, to maintain
> > + * the default dfn == pfn map? (See comment on dfn at the top of
> > + * include/xen/mm.h). Note that hap_pt_share == false does not
> > + * necessarily imply this is true.
> > */
> > bool need_sync;
> > };
> > @@ -275,8 +283,7 @@ struct domain_iommu {
> > #define iommu_clear_feature(d, f) clear_bit(f, dom_iommu(d)->features)
> >
> > /* Are we using the domain P2M table as its IOMMU pagetable? */
> > -#define iommu_use_hap_pt(d) \
> > - (hap_enabled(d) && is_iommu_enabled(d) && iommu_hap_pt_share)
> > +#define iommu_use_hap_pt(d) (dom_iommu(d)->hap_pt_share)
> >
> > /* Does the IOMMU pagetable need to be kept synchronized with the P2M */
> > #ifdef CONFIG_HAS_PASSTHROUGH
> >
>
> Cheers,
>
> --
> Julien Grall
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