[shadow] Disable higher level pagetables early unshadow only when the "process dying...

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>

diff --git a/xen/arch/x86/mm/shadow/multi.c b/xen/arch/x86/mm/shadow/multi.c
index 7731553e5365b77a623a1109e72be84a13279b60..7ccd38edd1150835a5b2216a803146ad64c20fb6 100644 (file)
--- a/xen/arch/x86/mm/shadow/multi.c
+++ b/xen/arch/x86/mm/shadow/multi.c
@@ -2728,8 +2728,9 @@ static inline void check_for_early_unshadow(struct vcpu *v, mfn_t gmfn)
            || ( !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 */ );