libxc: fix incorrect scanning of pfn array in pagebuf during migration

xc_domain_restore.c:apply_batch function makes two passes over the pfn_types
array in pagebuf to allocate the needed MFNs. The curbatch parameter to this
function specifies the array offset in pfn_types, from where the current scan
should begin. But this variable is not taken into account (index always starts
at 0) during the two passes. While this [bug] does not manifest itsef during
save/restore or live migration, under Remus, xc_domain_restore fails due to
corrupt guest page tables.

(This appears to have been broken by 21588:6c3d8aec202d which reverted
two changesets from before Remus support was added and hence
reintroduced some none-Remus compatible bits.)

Signed-off-by: Shriram Rajagopalan <rshriram@cs.ubc.ca>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/libxc/xc_domain_restore.c

@@ -907,8 +907,8 @@ static int apply_batch(xc_interface *xch, uint32_t dom, struct restore_ctx *ctx,
     for ( i = 0; i < j; i++ )
     {
         unsigned long pfn, pagetype;
-        pfn      = pagebuf->pfn_types[i] & ~XEN_DOMCTL_PFINFO_LTAB_MASK;
-        pagetype = pagebuf->pfn_types[i] &  XEN_DOMCTL_PFINFO_LTAB_MASK;
+        pfn      = pagebuf->pfn_types[i + curbatch] & ~XEN_DOMCTL_PFINFO_LTAB_MASK;
+        pagetype = pagebuf->pfn_types[i + curbatch] &  XEN_DOMCTL_PFINFO_LTAB_MASK;
 
         if ( (pagetype != XEN_DOMCTL_PFINFO_XTAB) && 
              (ctx->p2m[pfn] == INVALID_P2M_ENTRY) )
@@ -934,8 +934,8 @@ static int apply_batch(xc_interface *xch, uint32_t dom, struct restore_ctx *ctx,
     for ( i = 0; i < j; i++ )
     {
         unsigned long pfn, pagetype;
-        pfn      = pagebuf->pfn_types[i] & ~XEN_DOMCTL_PFINFO_LTAB_MASK;
-        pagetype = pagebuf->pfn_types[i] &  XEN_DOMCTL_PFINFO_LTAB_MASK;
+        pfn      = pagebuf->pfn_types[i + curbatch] & ~XEN_DOMCTL_PFINFO_LTAB_MASK;
+        pagetype = pagebuf->pfn_types[i + curbatch] &  XEN_DOMCTL_PFINFO_LTAB_MASK;
 
         if ( pagetype == XEN_DOMCTL_PFINFO_XTAB )
             region_mfn[i] = ~0UL; /* map will fail but we don't care */