[Xen-devel] [PATCH RFC] xen/grant_table: deprecate GNTTABOP_unmap_and_replace

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

GNTTABOP_unmap_and_replace has two issues:
- it unconditionally replaces the mapping passed in new_addr with 0;
- it doesn't support GNTMAP_contains_pte mappings on x86, returning a
general error instead of some forms of ENOSYS.

Deprecate GNTTABOP_unmap_and_replace and introduce a new
GNTTABOP_unmap_and_replace (12) that returns GNTST_enosys for
GNTMAP_contains_pte requests and doesn't zero the mapping at new_addr.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
---
 xen/arch/x86/mm.c                |   12 +-----------
 xen/include/public/grant_table.h |    7 ++++---
 2 files changed, 5 insertions(+), 14 deletions(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 77dcafc..610fd09 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -4064,7 +4064,7 @@ int replace_grant_host_mapping(
             return destroy_grant_pte_mapping(addr, frame, curr->domain);
         
         MEM_LOG("Unsupported grant table operation");
-        return GNTST_general_error;
+        return GNTST_enosys;
     }
 
     if ( !new_addr )
@@ -4102,16 +4102,6 @@ int replace_grant_host_mapping(
 
     ol1e = *pl1e;
 
-    if ( unlikely(!UPDATE_ENTRY(l1, pl1e, ol1e, l1e_empty(),
-                                gl1mfn, curr, 0)) )
-    {
-        page_unlock(l1pg);
-        put_page(l1pg);
-        MEM_LOG("Cannot delete PTE entry at %p", (unsigned long *)pl1e);
-        guest_unmap_l1e(curr, pl1e);
-        return GNTST_general_error;
-    }
-
     page_unlock(l1pg);
     put_page(l1pg);
     guest_unmap_l1e(curr, pl1e);
diff --git a/xen/include/public/grant_table.h b/xen/include/public/grant_table.h
index b8a3d6c..ae841ae 100644
--- a/xen/include/public/grant_table.h
+++ b/xen/include/public/grant_table.h
@@ -303,12 +303,13 @@ typedef uint16_t grant_status_t;
 #define GNTTABOP_transfer             4
 #define GNTTABOP_copy                 5
 #define GNTTABOP_query_size           6
-#define GNTTABOP_unmap_and_replace    7
+#define GNTTABOP_unmap_and_replace_legacy    7
 #if __XEN_INTERFACE_VERSION__ >= 0x0003020a
 #define GNTTABOP_set_version          8
 #define GNTTABOP_get_status_frames    9
 #define GNTTABOP_get_version          10
 #define GNTTABOP_swap_grant_ref              11
+#define GNTTABOP_unmap_and_replace    12
 #endif /* __XEN_INTERFACE_VERSION__ */
 /* ` } */
 
@@ -489,8 +490,7 @@ DEFINE_XEN_GUEST_HANDLE(gnttab_query_size_t);
 /*
  * GNTTABOP_unmap_and_replace: Destroy one or more grant-reference mappings
  * tracked by <handle> but atomically replace the page table entry with one
- * pointing to the machine address under <new_addr>.  <new_addr> will be
- * redirected to the null entry.
+ * pointing to the machine address under <new_addr>.
  * NOTES:
  *  1. The call may fail in an undefined manner if either mapping is not
  *     tracked by <handle>.
@@ -631,6 +631,7 @@ DEFINE_XEN_GUEST_HANDLE(gnttab_swap_grant_ref_t);
 #define GNTST_bad_copy_arg    (-10) /* copy arguments cross page boundary.   */
 #define GNTST_address_too_big (-11) /* transfer page address too large.      */
 #define GNTST_eagain          (-12) /* Operation not done; try again.        */
+#define GNTST_enosys          (-13) /* Operation not implemented.            */
 /* ` } */
 
 #define GNTTABOP_error_msgs {                   \
-- 
1.7.2.5


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