Re: [Xen-devel] [v3][PATCH 03/16] xen/vtd: create RMRR mapping

["Chen, Tiejun" <tiejun.chen@xxxxxxxxx>]

On 2015/6/12 10:43, Chen, Tiejun wrote:
> On 2015/6/11 22:07, Tim Deegan wrote:
> > At 17:31 +0800 on 11 Jun (1434043916), Chen, Tiejun wrote:
> > > > >        while ( base_pfn < end_pfn )
> > > > >        {
> > > > > -        int err = intel_iommu_map_page(d, base_pfn, base_pfn,
> > > > > -
> > > > > IOMMUF_readable|IOMMUF_writable);
> > > > > +        int err = set_identity_p2m_entry(d, base_pfn, p2m_access_rw);
> > > > >
> > > > >            if ( err )
> > > > >                return err;
> > > > Tim has another comment to replace earlier unmap with
> > > Yes, I knew this.
> > >
> > > > guest_physmap_remove_page() which will call iommu
> > > > unmap internally. Please include this change too.
> > > But,
> > >
> > > guest_physmap_remove_page()
> > >       |
> > >       + p2m_remove_page()
> > >     |
> > >     + iommu_unmap_page()
> > >     |
> > >     + p2m_set_entry(p2m, gfn, _mfn(INVALID_MFN), xxx)
> > >
> > > I think this already remove these pages both on ept/vt-d sides, right?
> > Yes; this is about this code further up in the same function:
> >
> >             while ( base_pfn < end_pfn )
> >             {
> >                 if ( intel_iommu_unmap_page(d, base_pfn) )
> >                     ret = -ENXIO;
> >                 base_pfn++;
> >             }
> >
> > which ought to be calling guest_physmap_remove_page() or similar, to
> > make sure that both iommu and EPT mappings get removed.
> I still just think current implementation might be fine at this point.
>
> We have two scenarios here, the case of shared ept and the case of
> non-shared ept. But no matter what case we're tracking, shouldn't
> guest_physmap_remove_page() always call p2m->set_entry() to clear *all*
> *valid* mfn which is owned by a given VM? And p2m->set_entry() also
> calls iommu_unmap_page() internally. So nothing special should further
> consider.
>
> If I'm wrong or misunderstanding, please correct me :)
Sorry for my misunderstanding to this. Right now Kevin help me 
understand what you mean. Sounds like we should address something 
specific to unmap rmrr here.
So I will do this as follows:

#1. Provide a clear helper

+int clear_identity_p2m_entry(struct domain *d, unsigned long gfn,
+                             unsigned int page_order)
+{
+    struct p2m_domain *p2m = p2m_get_hostp2m(d);
+    int ret;
+    gfn_lock(p2m, gfn, page_order);
+    ret = p2m_remove_page(p2m, gfn, gfn, page_order);
+    gfn_unlock(p2m, gfn, page_order);
+    return ret;
+}
+

#2. Call such a helper

@@ -1840,7 +1840,7 @@ static int rmrr_identity_mapping(struct domain *d, 
bool_t map,
             while ( base_pfn < end_pfn )
             {
-                if ( intel_iommu_unmap_page(d, base_pfn) )
+                if ( clear_identity_p2m_entry(d, base_pfn, 0) )
                     ret = -ENXIO;
                 base_pfn++;
             }
Is this right?

Thanks
Tiejun

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