xen: arm: avoid reusing incorrect mappings when walking the p2m.

When we change which PT page we are mapping at a given level then we need to
invalidate any cached mappings further down the tree, otherwise we risk using
them because their offset might match but be based on a different offset
further up the table.

e.g. when remapping first then cur_first_offset and cur_second_offset (which
indicate the currently mapped second and third tables respectively) both become
invalid

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Julien Grall <julien.grall@linaro.org>

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index 2f855b5d5c44ec5d2986ca42d54a286a37338289..8ffddacb062481b5f83a55df6b9da25354fb652a 100644 (file)
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -743,6 +743,8 @@ static int apply_p2m_changes(struct domain *d,
                 goto out;
             }
             cur_first_page = p2m_first_level_index(addr);
+            /* Any mapping further down is now invalid */
+            cur_first_offset = cur_second_offset = ~0;
         }
 
         /* We only use a 3 level p2m at the moment, so no level 0,
@@ -765,6 +767,8 @@ static int apply_p2m_changes(struct domain *d,
             if (second) unmap_domain_page(second);
             second = map_domain_page(first[first_table_offset(addr)].p2m.base);
             cur_first_offset = first_table_offset(addr);
+            /* Any mapping further down is now invalid */
+            cur_second_offset = ~0;
         }
         /* else: second already valid */