Re: [Xen-devel] Regression in RMRRs identity mapping for PVH Dom0

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 24.09.15 at 11:18, <tim@xxxxxxx> wrote:
> AIUI the problem is that before the call to set_identity_p2m_entry(),
> PVH dom0 has a p2m entry covering this range but no IOMMU entry.  Is
> that right?  So the fix will be to make PVH dom0 construction set up
> the IOMMU correctly when it sets up the p2m.

Right, but with the current way of setting up PVH Dom0 I'm afraid
this will be rather intrusive to implement. Hence, however much I
dislike it, I wonder whether a variant of Elena's change (suitably
annotated with a phv fixme) wouldn't be a reasonable thing for 4.6.
With the switch to HVMlite the Dom0 setup will need to be re-done
anyway afaics.

Elena, as to the actual patch:

>--- a/xen/arch/x86/mm/p2m.c
>+++ b/xen/arch/x86/mm/p2m.c
>@@ -970,8 +970,10 @@ int set_identity_p2m_entry(struct domain *d, unsigned 
>long gfn,
>     if ( p2mt == p2m_invalid || p2mt == p2m_mmio_dm )
>         ret = p2m_set_entry(p2m, gfn, _mfn(gfn), PAGE_ORDER_4K,
>                             p2m_mmio_direct, p2ma);
>-    else if ( mfn_x(mfn) == gfn && p2mt == p2m_mmio_direct && a == p2ma )
>-        ret = 0;
>+    else if ( mfn_x(mfn) == gfn && p2mt == p2m_mmio_direct )
>+        if ( a == p2ma && !is_pvh_domain(d) )
>+            ret = 0;
>+        else ret = iommu_map_page(d, gfn, gfn, 
>IOMMUF_readable|IOMMUF_writable);

Besides this wanting figure braces, why do you pull the a == p2ma
check into the inner if()? If this is because of the P2M getting
populated with p2m_rwx, I think _that_ should be changed rather
than breaking the logic here (or, if done properly, complicating it).
There's no reason I can see to map MMIO regions rwx.

Also I think this wants to cover just hwdom and !iommu_use_hap_pt.

Jan

>     else
>     {
>         if ( flag & XEN_DOMCTL_DEV_RDM_RELAXED )



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