x86/HAP: move nested-P2M flush calculations out of locked region

By latching the old MFN into a local variable, these calculations don't
depend on anything but local variables anymore. Hence the point in time
when they get performed doesn't matter anymore, so they can be moved
past the locked region.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>

diff --git a/xen/arch/x86/mm/hap/hap.c b/xen/arch/x86/mm/hap/hap.c
index 69b06f19b5f1ffac70049e319060d327f401c7cd..d1ad10003c312d8e841907ad91940acb8b719419 100644 (file)
--- a/xen/arch/x86/mm/hap/hap.c
+++ b/xen/arch/x86/mm/hap/hap.c
@@ -780,7 +780,7 @@ hap_write_p2m_entry(struct p2m_domain *p2m, unsigned long gfn, l1_pgentry_t *p,
 {
     struct domain *d = p2m->domain;
     uint32_t old_flags;
-    bool_t flush_nestedp2m = 0;
+    mfn_t omfn;
     int rc;
 
     /* We know always use the host p2m here, regardless if the vcpu
@@ -790,21 +790,11 @@ hap_write_p2m_entry(struct p2m_domain *p2m, unsigned long gfn, l1_pgentry_t *p,
 
     paging_lock(d);
     old_flags = l1e_get_flags(*p);
-
-    if ( nestedhvm_enabled(d) && (old_flags & _PAGE_PRESENT) 
-         && !p2m_get_hostp2m(d)->defer_nested_flush ) {
-        /* We are replacing a valid entry so we need to flush nested p2ms,
-         * unless the only change is an increase in access rights. */
-        mfn_t omfn = l1e_get_mfn(*p);
-        mfn_t nmfn = l1e_get_mfn(new);
-
-        flush_nestedp2m = !(mfn_eq(omfn, nmfn)
-            && perms_strictly_increased(old_flags, l1e_get_flags(new)) );
-    }
+    omfn = l1e_get_mfn(*p);
 
     rc = p2m_entry_modify(p2m, p2m_flags_to_type(l1e_get_flags(new)),
                           p2m_flags_to_type(old_flags), l1e_get_mfn(new),
-                          l1e_get_mfn(*p), level);
+                          omfn, level);
     if ( rc )
     {
         paging_unlock(d);
@@ -817,7 +807,14 @@ hap_write_p2m_entry(struct p2m_domain *p2m, unsigned long gfn, l1_pgentry_t *p,
 
     paging_unlock(d);
 
-    if ( flush_nestedp2m )
+    if ( nestedhvm_enabled(d) && (old_flags & _PAGE_PRESENT) &&
+         !p2m_get_hostp2m(d)->defer_nested_flush &&
+         /*
+          * We are replacing a valid entry so we need to flush nested p2ms,
+          * unless the only change is an increase in access rights.
+          */
+         (!mfn_eq(omfn, l1e_get_mfn(new)) ||
+          !perms_strictly_increased(old_flags, l1e_get_flags(new))) )
         p2m_flush_nestedp2m(d);
 
     return 0;