[Xen-devel] [PATCH for-4.12 v2 4/8] xen/arm: Add support for read-only foreign mappings

[Julien Grall <julien.grall@xxxxxxx>]

Current, foreign mappings can only be read-write. A follow-up patch will
extend foreign mapping for Xen backend memory (via XEN_DOMID), some of
that memory should only be read accessible for the mapping domain.

Introduce a new p2m_type to cater read-only foreign mappings. For now,
the decision between the two foreign mapping type is based on the type
of the guest page mapped.

Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
Reviewed-by: Andrii Anisov <andrii_anisov@xxxxxxxx>

---

    Changes in v2:
        - Add Andrii's reviewed-by
---
 xen/arch/arm/mm.c         |  2 +-
 xen/arch/arm/p2m.c        |  1 +
 xen/include/asm-arm/p2m.h | 42 +++++++++++++++++++++++++++++++++++++++---
 3 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 7193d83b44..58f7e54640 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -1267,7 +1267,7 @@ int xenmem_add_to_physmap_one(
         }
 
         mfn = page_to_mfn(page);
-        t = p2m_map_foreign_rw;
+        t = (p2mt == p2m_ram_rw) ? p2m_map_foreign_rw : p2m_map_foreign_ro;
 
         rcu_unlock_domain(od);
         break;
diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index e0b84a9db5..dea04ef66f 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -477,6 +477,7 @@ static void p2m_set_permission(lpae_t *e, p2m_type_t t, 
p2m_access_t a)
         break;
 
     case p2m_iommu_map_ro:
+    case p2m_map_foreign_ro:
     case p2m_grant_map_ro:
     case p2m_invalid:
         e->p2m.xn = 1;
diff --git a/xen/include/asm-arm/p2m.h b/xen/include/asm-arm/p2m.h
index a1aef7b793..6f2728e2bb 100644
--- a/xen/include/asm-arm/p2m.h
+++ b/xen/include/asm-arm/p2m.h
@@ -116,6 +116,7 @@ typedef enum {
     p2m_mmio_direct_nc, /* Read/write mapping of genuine MMIO area 
non-cacheable */
     p2m_mmio_direct_c,  /* Read/write mapping of genuine MMIO area cacheable */
     p2m_map_foreign_rw, /* Read/write RAM pages from foreign domain */
+    p2m_map_foreign_ro, /* Read-only RAM pages from foreign domain */
     p2m_grant_map_rw,   /* Read/write grant mapping */
     p2m_grant_map_ro,   /* Read-only grant mapping */
     /* The types below are only used to decide the page attribute in the P2M */
@@ -135,12 +136,16 @@ typedef enum {
 #define P2M_GRANT_TYPES (p2m_to_mask(p2m_grant_map_rw) |  \
                          p2m_to_mask(p2m_grant_map_ro))
 
+/* Foreign mappings types */
+#define P2M_FOREIGN_TYPES (p2m_to_mask(p2m_map_foreign_rw) | \
+                           p2m_to_mask(p2m_map_foreign_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_rw))
+#define p2m_is_foreign(_t) (p2m_to_mask(_t) & P2M_FOREIGN_TYPES)
 #define p2m_is_any_ram(_t) (p2m_to_mask(_t) &                   \
                             (P2M_RAM_TYPES | P2M_GRANT_TYPES |  \
-                             p2m_to_mask(p2m_map_foreign_rw)))
+                             P2M_FOREIGN_TYPES))
 
 /* All common type definitions should live ahead of this inclusion. */
 #ifdef _XEN_P2M_COMMON_H
@@ -295,7 +300,38 @@ struct page_info *p2m_get_page_from_gfn(struct domain *d, 
gfn_t gfn,
 static inline struct page_info *get_page_from_gfn(
     struct domain *d, unsigned long gfn, p2m_type_t *t, p2m_query_t q)
 {
-    return p2m_get_page_from_gfn(d, _gfn(gfn), t);
+    mfn_t mfn;
+    p2m_type_t _t;
+    struct page_info *page;
+
+    /*
+     * Special case for DOMID_XEN as it is the only domain so far that is
+     * not auto-translated.
+     */
+    if ( unlikely(d != dom_xen) )
+        return p2m_get_page_from_gfn(d, _gfn(gfn), t);
+
+    if ( !t )
+        t = &_t;
+
+    *t = p2m_invalid;
+
+    /*
+     * DOMID_XEN see 1-1 RAM. The p2m_type is based on the type of the
+     * page.
+     */
+    mfn = _mfn(gfn);
+    page = mfn_to_page(mfn);
+
+    if ( !mfn_valid(mfn) || !get_page(page, d) )
+        return NULL;
+
+    if ( page->u.inuse.type_info & PGT_writable_page )
+        *t = p2m_ram_rw;
+    else
+        *t = p2m_ram_ro;
+
+    return page;
 }
 
 int get_page_type(struct page_info *page, unsigned long type);
-- 
2.11.0


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel