[PATCH] x86/pvh: fix population of the low 1MB for dom0

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

RMRRs are setup ahead of populating the p2m and hence the ASSERT when
populating the low 1MB needs to be relaxed when it finds an existing
entry: it's either RAM or a RMRR resulting from the IOMMU setup.

Rework the logic a bit and introduce a local mfn variable in order to
assert that if the gfn is populated and not RAM it is an identity map.

Fixes: 6b4f6a31ac ('x86/PVH: de-duplicate mappings for first Mb of Dom0 memory')
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/hvm/dom0_build.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/hvm/dom0_build.c b/xen/arch/x86/hvm/dom0_build.c
index b00e45885c..739bb8adb6 100644
--- a/xen/arch/x86/hvm/dom0_build.c
+++ b/xen/arch/x86/hvm/dom0_build.c
@@ -466,11 +466,17 @@ static int __init pvh_populate_p2m(struct domain *d)
     for ( i = rc = 0; i < MB1_PAGES; ++i )
     {
         p2m_type_t p2mt;
+        mfn_t mfn;
 
-        if ( mfn_eq(get_gfn_query(d, i, &p2mt), INVALID_MFN) )
+        mfn = get_gfn_query(d, i, &p2mt);
+        if ( mfn_eq(mfn, INVALID_MFN) )
             rc = set_mmio_p2m_entry(d, _gfn(i), _mfn(i), PAGE_ORDER_4K);
-        else
-            ASSERT(p2mt == p2m_ram_rw);
+        else if ( p2mt != p2m_ram_rw && !mfn_eq(mfn, _mfn(i)) )
+                /*
+                 * If the p2m entry is already set it must belong to a RMRR and
+                 * already be identity mapped, or be a RAM region.
+                 */
+                ASSERT_UNREACHABLE();
         put_gfn(d, i);
         if ( rc )
         {
-- 
2.34.1