References: bnc#726332

# HG changeset patch
# User Gianluca Guida <gianluca.guida@citrix.com>
# Date 1321456773 0
# Node ID 3ecc8fef428138e4304ef11b47498981e63626b3
# Parent  a5f1d3b1612bb48e1cb09dc66b0909e3613dc855
[shadow] Disable higher level pagetables early unshadow only when the "process dying" hypercall is used.

This patch fixes a performance problem in fully virtualized guests.

Signed-off-by: Gianluca Guida <gianluca.guida@citrix.com>
Tested-by: Jan Beulich <jbeulich@suse.com>
Committed-by: Keir Fraser <keir@xen.org>

--- a/xen/arch/x86/mm/shadow/multi.c
+++ b/xen/arch/x86/mm/shadow/multi.c
@@ -2743,8 +2743,9 @@ static inline void check_for_early_unsha
            || ( !v->domain->arch.paging.shadow.pagetable_dying_op
                 && v->arch.paging.shadow.last_emulated_mfn_for_unshadow == mfn_x(gmfn) ) )
          && sh_mfn_is_a_page_table(gmfn)
-         && !(mfn_to_page(gmfn)->shadow_flags
-              & (SHF_L2_32|SHF_L2_PAE|SHF_L2H_PAE|SHF_L4_64)) )
+         && (!v->domain->arch.paging.shadow.pagetable_dying_op ||
+             !(mfn_to_page(gmfn)->shadow_flags
+               & (SHF_L2_32|SHF_L2_PAE|SHF_L2H_PAE|SHF_L4_64))) )
     {
         perfc_incr(shadow_early_unshadow);
         sh_remove_shadows(v, gmfn, 1, 0 /* Fast, can fail to unshadow */ );