x86/mm: Eliminate hash table in sharing code as index of shared mfns

Eliminate the sharing hastable mechanism by storing a list head directly in the
page info for the case when the page is shared.  This does not add any extra
space to the page_info and serves to remove significant complexity from
sharing.

Signed-off-by: Adin Scannell <adin@scannell.ca>
Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.org>
Acked-by: Tim Deegan <tim@xen.org>
Committed-by: Tim Deegan <tim@xen.org>

1 files changed, 9 insertions, 2 deletions

diff --git a/xen/include/asm-x86/mm.h b/xen/include/asm-x86/mm.h
index 40dbbf61e4..b23479c481 100644
--- a/xen/include/asm-x86/mm.h
+++ b/xen/include/asm-x86/mm.h
@@ -31,6 +31,8 @@ struct page_list_entry
     __pdx_t next, prev;
 };
 
+struct page_sharing_info;
+
 struct page_info
 {
     union {
@@ -49,8 +51,13 @@ struct page_info
         /* For non-pinnable single-page shadows, a higher entry that points
          * at us. */
         paddr_t up;
-        /* For shared/sharable pages the sharing handle */
-        uint64_t shr_handle; 
+        /* For shared/sharable pages, we use a doubly-linked list
+         * of all the {pfn,domain} pairs that map this page. We also include
+         * an opaque handle, which is effectively a version, so that clients
+         * of sharing share the version they expect to.
+         * This list is allocated and freed when a page is shared/unshared.
+         */
+        struct page_sharing_info *shared_info;
     };
 
     /* Reference count and various PGC_xxx flags and fields. */