Re: [Xen-devel] [PATCH] x86/p2m: fix non-translated handling of iommu mappings

[Jan Beulich <JBeulich@xxxxxxxx>]

On 22.07.2019 17:32, Roger Pau Monne wrote:
> The current usage of need_iommu_pt_sync in p2m for non-translated
> guests is wrong because it doesn't correctly handle a relaxed PV
> hardware domain, that has need_sync set to false, but still need
> entries to be added from calls to {set/clear}_identity_p2m_entry.
> 
> Adjust the code in guest_physmap_add_page to also check whether the
> domain has an iommu instead of whether it needs syncing or not in
> order to take a reference to a page to be mapped.

Why this seemingly unrelated change? I ask because ...

> --- a/xen/arch/x86/mm/p2m.c
> +++ b/xen/arch/x86/mm/p2m.c
> @@ -836,7 +836,7 @@ guest_physmap_add_page(struct domain *d, gfn_t gfn, mfn_t 
> mfn,
>            */
>           for ( i = 0; i < (1UL << page_order); ++i, ++page )
>           {
> -            if ( !need_iommu_pt_sync(d) )
> +            if ( !has_iommu_pt(d) )
>                   /* nothing */;
>               else if ( get_page_and_type(page, d, PGT_writable_page) )
>                   put_page_and_type(page);

... this parallels the code in iommu_hwdom_init(), which similarly
uses need_iommu_pt_sync() (and during the prior discussion you did
agree with Paul that it shouldn't be changed). IOW the patch for
now can have my R-b only with this change and the respective part
of the description dropped.

Jan
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