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

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@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 2d5fc9120d556ec3c4b1acf0ab5660a6d3f7ebeb
master date: 2022-01-25 10:52:24 +0000

diff --git a/xen/arch/x86/hvm/dom0_build.c b/xen/arch/x86/hvm/dom0_build.c
index 01b1356bd2b800b35de773144b901205e8405d9c..453f115847b0bbc94377de4d077e16b0e49e6f4e 100644 (file)
--- a/xen/arch/x86/hvm/dom0_build.c
+++ b/xen/arch/x86/hvm/dom0_build.c
@@ -465,11 +465,16 @@ static int __init pvh_populate_p2m(struct domain *d)
     for ( i = rc = 0; i < MB1_PAGES; ++i )
     {
         p2m_type_t p2mt;
+        mfn_t mfn = get_gfn_query(d, i, &p2mt);
 
-        if ( mfn_eq(get_gfn_query(d, i, &p2mt), INVALID_MFN) )
+        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);
+            /*
+             * If the p2m entry is already set it must belong to a RMRR and
+             * already be identity mapped, or be a RAM region.
+             */
+            ASSERT(p2mt == p2m_ram_rw || mfn_eq(mfn, _mfn(i)));
         put_gfn(d, i);
         if ( rc )
         {