[Xen-devel] [PATCH v2 02/15] xen/arm: p2m: Use a whitelist rather than blacklist in get_page_from_gfn

[Julien Grall <julien.grall@xxxxxxx>]

Currently, the check in get_page_from_gfn is using a blacklist. This is
very fragile because we may forgot to update the check when a new p2m
type is added.

To avoid any possible issue, use a whitelist. All type backed by a RAM
page can could potential be valid. The check is borrowed from x86.

Note with this change, it is not possible anymore to retrieve a page when
the p2m type is p2m_iommu_map_*. This is fine because they are special
mappings for direct mapping workaround and the associated GFN should be
used at all by callers of get_page_from_gfn.

Signed-off-by: Julien Grall <julien.grall@xxxxxxx>

---
    Changes in v2:
        - Update the commit message about iommu_mappings
---
 xen/include/asm-arm/p2m.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/xen/include/asm-arm/p2m.h b/xen/include/asm-arm/p2m.h
index 3091c04..78d37ab 100644
--- a/xen/include/asm-arm/p2m.h
+++ b/xen/include/asm-arm/p2m.h
@@ -104,9 +104,16 @@ typedef enum {
 #define P2M_RAM_TYPES (p2m_to_mask(p2m_ram_rw) |        \
                        p2m_to_mask(p2m_ram_ro))
 
+/* Grant mapping types, which map to a real frame in another VM */
+#define P2M_GRANT_TYPES (p2m_to_mask(p2m_grant_map_rw) |  \
+                         p2m_to_mask(p2m_grant_map_ro))
+
 /* Useful predicates */
 #define p2m_is_ram(_t) (p2m_to_mask(_t) & P2M_RAM_TYPES)
 #define p2m_is_foreign(_t) (p2m_to_mask(_t) & p2m_to_mask(p2m_map_foreign))
+#define p2m_is_any_ram(_t) (p2m_to_mask(_t) &                   \
+                            (P2M_RAM_TYPES | P2M_GRANT_TYPES |  \
+                             p2m_to_mask(p2m_map_foreign)))
 
 static inline
 void p2m_mem_access_emulate_check(struct vcpu *v,
@@ -224,7 +231,7 @@ static inline struct page_info *get_page_from_gfn(
     if (t)
         *t = p2mt;
 
-    if ( p2mt == p2m_invalid || p2mt == p2m_mmio_direct )
+    if ( !p2m_is_any_ram(p2mt) )
         return NULL;
 
     if ( !mfn_valid(mfn) )
-- 
1.9.1


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