[Xen-devel] [PATCH 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>
---
 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 cec821c3a3..e31b47a394 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -1283,7 +1283,7 @@ 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 b32b16cd94..0941be9e41 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -450,6 +450,7 @@ 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 5f7f31186d..7c67806056 100644
--- a/xen/include/asm-arm/p2m.h
+++ b/xen/include/asm-arm/p2m.h
@@ -118,6 +118,7 @@ enum p2m_type {
     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 */
@@ -137,12 +138,16 @@ enum p2m_type {
 #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))
 
 static inline
 void p2m_altp2m_check(struct vcpu *v, uint16_t idx)
@@ -275,7 +280,38 @@ 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


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