[Xen-devel] [PATCH v4 07/10] xen/arm: page: Describe the layout of flags used to update page tables

[Julien Grall <julien.grall@xxxxxxx>]

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 <julien.grall@xxxxxxx>
Reviewed-by: Andre Przywara <andre.przywara@xxxxxxx>
Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

---
    Changes in v4:
        - Use PAGE_AI_MASK in set_fixmap

    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          | 4 ++--
 xen/include/asm-arm/page.h | 7 +++++++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 70a03015ec..c1dad61a20 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -331,7 +331,7 @@ static inline lpae_t mfn_to_xen_entry(mfn_t mfn, unsigned 
attr)
 /* Map a 4k page in a fixmap entry */
 void set_fixmap(unsigned map, mfn_t mfn, unsigned int flags)
 {
-    lpae_t pte = mfn_to_xen_entry(mfn, flags);
+    lpae_t pte = mfn_to_xen_entry(mfn, PAGE_AI_MASK(flags));
     pte.pt.table = 1; /* 4k mappings always have this bit set */
     pte.pt.xn = 1;
     write_pte(xen_fixmap + third_table_offset(FIXMAP_ADDR(map)), pte);
@@ -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)
-- 
2.11.0


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