[v3,6/9] xen/arm: page: Describe the layout of flags used to update page tables

Commit Message

Julien Grall Oct. 2, 2017, 5:31 p.m. UTC

Currently, the flags used to update page tables (i.e PAGE_HYPERVISOR_*)
only contains the memory attribute index. Follow-up patches will add
more information in it. So document the current layout.

At the same time introduce PAGE_AI_MASK to get the memory attribute
index easily.

Signed-off-by: Julien Grall <[e-mail]>
Reviewed-by: Andre Przywara <[e-mail]>
Reviewed-by: Stefano Stabellini <[e-mail]>

---
    Changes in v3:
        - Add Stefano's reviewed-by

    Changes in v2:
        - Slightly update the commit message to specify we describe the
        current layout.
        - Add Andre's reviewed-by
---
 xen/arch/arm/mm.c          | 2 +-
 xen/include/asm-arm/page.h | 7 +++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

Patch

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 39bade63f5..117f05a1d6 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -1021,7 +1021,7 @@  static int create_xen_entries(enum xenmap_operation op,
                 }
                 if ( op == RESERVE )
                     break;
-                pte = mfn_to_xen_entry(mfn, flags);
+                pte = mfn_to_xen_entry(mfn, PAGE_AI_MASK(flags));
                 pte.pt.table = 1;
                 write_pte(entry, pte);
                 break;
diff --git a/xen/include/asm-arm/page.h b/xen/include/asm-arm/page.h
index 0ae1a2587b..aa3e83f5b4 100644
--- a/xen/include/asm-arm/page.h
+++ b/xen/include/asm-arm/page.h
@@ -65,6 +65,13 @@ 
 #define MAIR0VAL (MAIRVAL & 0xffffffff)
 #define MAIR1VAL (MAIRVAL >> 32)
 
+/*
+ * Layout of the flags used for updating the hypervisor page tables
+ *
+ * [0:2] Memory Attribute Index
+ */
+#define PAGE_AI_MASK(x) ((x) & 0x7U)
+
 #define PAGE_HYPERVISOR         (MT_NORMAL)
 #define PAGE_HYPERVISOR_NOCACHE (MT_DEVICE_nGnRE)
 #define PAGE_HYPERVISOR_WC      (MT_NORMAL_NC)