[xen staging] x86/HAP: move nested-P2M flush calculations out of locked region

[patchbot@xxxxxxx]

commit a7ab52f9e87c5140b8f0c5444c79d061a6985a2b
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Wed Nov 18 12:34:54 2020 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Nov 18 12:34:54 2020 +0100

    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@xxxxxxxx>
    Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/mm/hap/hap.c | 25 +++++++++++--------------
 1 file changed, 11 insertions(+), 14 deletions(-)

diff --git a/xen/arch/x86/mm/hap/hap.c b/xen/arch/x86/mm/hap/hap.c
index 69b06f19b5..d1ad10003c 100644
--- 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;
--
generated by git-patchbot for /home/xen/git/xen.git#staging