[PATCH v1 1/3] xen/arm: generalize per-page GFN storage beyond xenheap pages

[Penny Zheng <Penny.Zheng@xxxxxxx>]

As preparation for fixing mfn_to_gfn() on ARM, we extend the existing GFN
field in page_info's type_info to be usable for not only xenheap ones.
Another usage will be introduced later for stolen pages in memory exchaging.

Introduce general-purpose page_get_gfn() and page_set_gfn() helpers
that read and write the GFN stored in type_info. The old
page_get_xenheap_gfn() and page_set_xenheap_gfn() are retained as thin
wrappers with their xenheap ASSERTs, so all current callers remain unchanged.

Also introduce PGT_INVALID_GFN as the general sentinel, with
PGT_INVALID_XENHEAP_GFN aliased to it for backward compatibility.

Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx>
---
 xen/arch/arm/include/asm/mm.h | 37 +++++++++++++++++++++++------------
 1 file changed, 25 insertions(+), 12 deletions(-)

diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h
index 72a6928624..d1873ec212 100644
--- a/xen/arch/arm/include/asm/mm.h
+++ b/xen/arch/arm/include/asm/mm.h
@@ -113,18 +113,21 @@ struct page_info
 #define PGT_count_mask    PG_mask(3, 3)
 
 /*
- * Stored in bits [28:0] (arm32) or [60:0] (arm64) GFN if page is xenheap page.
+ * Stored in bits [28:0] (arm32) or [60:0] (arm64) GFN if page is xenheap page,
+ * or stolen ones in memory exchanging.
  */
 #define PGT_gfn_width     PG_shift(3)
 #define PGT_gfn_mask      ((1UL<<PGT_gfn_width)-1)
 
-#define PGT_INVALID_XENHEAP_GFN   _gfn(PGT_gfn_mask)
+#define PGT_INVALID_GFN           _gfn(PGT_gfn_mask)
+#define PGT_INVALID_XENHEAP_GFN   PGT_INVALID_GFN
 
 /*
  * An arch-specific initialization pattern is needed for the type_info field
- * as it's GFN portion can contain the valid GFN if page is xenheap page.
+ * as it's GFN portion can contain the valid GFN if page is xenheap page, or
+ * stolen in memory exchanging.
  */
-#define PGT_TYPE_INFO_INITIALIZER   gfn_x(PGT_INVALID_XENHEAP_GFN)
+#define PGT_TYPE_INFO_INITIALIZER   gfn_x(PGT_INVALID_GFN)
 
  /* Cleared when the owning guest 'frees' this page. */
 #define _PGC_allocated    PG_shift(1)
@@ -338,28 +341,38 @@ unsigned int arch_get_dma_bitsize(void);
  * that requirement (risk of deadlock, lock inversion, etc) it is important
  * to make sure that all non-protected updates to this field are atomic.
  */
-static inline gfn_t page_get_xenheap_gfn(const struct page_info *p)
+static inline gfn_t page_get_gfn(const struct page_info *p)
 {
     gfn_t gfn_ = _gfn(ACCESS_ONCE(p->u.inuse.type_info) & PGT_gfn_mask);
 
-    ASSERT(is_xen_heap_page(p));
-
-    return gfn_eq(gfn_, PGT_INVALID_XENHEAP_GFN) ? INVALID_GFN : gfn_;
+    return gfn_eq(gfn_, PGT_INVALID_GFN) ? INVALID_GFN : gfn_;
 }
 
-static inline void page_set_xenheap_gfn(struct page_info *p, gfn_t gfn)
+static inline void page_set_gfn(struct page_info *p, gfn_t gfn)
 {
-    gfn_t gfn_ = gfn_eq(gfn, INVALID_GFN) ? PGT_INVALID_XENHEAP_GFN : gfn;
+    gfn_t gfn_ = gfn_eq(gfn, INVALID_GFN) ? PGT_INVALID_GFN : gfn;
     unsigned long x, nx, y = p->u.inuse.type_info;
 
-    ASSERT(is_xen_heap_page(p));
-
     do {
         x = y;
         nx = (x & ~PGT_gfn_mask) | gfn_x(gfn_);
     } while ( (y = cmpxchg(&p->u.inuse.type_info, x, nx)) != x );
 }
 
+static inline gfn_t page_get_xenheap_gfn(const struct page_info *p)
+{
+    ASSERT(is_xen_heap_page(p));
+
+    return page_get_gfn(p);
+}
+
+static inline void page_set_xenheap_gfn(struct page_info *p, gfn_t gfn)
+{
+    ASSERT(is_xen_heap_page(p));
+
+    page_set_gfn(p, gfn);
+}
+
 #endif /*  __ARCH_ARM_MM__ */
 /*
  * Local variables:
-- 
2.43.0