[xen staging] x86/mm: Remove unnecessary mfn_valid() call from get_page_from_l1e()

[patchbot@xxxxxxx]

commit c154abe99d45fad110384e1ea75fad50b65962b3
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Wed Apr 27 14:43:28 2022 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Wed May 18 15:05:18 2022 +0100

    x86/mm: Remove unnecessary mfn_valid() call from get_page_from_l1e()
    
    mfn_valid() is not a trivially simple, and contains an evaluate_nospec() for
    speculative defence.  Avoid calling it redundantly, and just store the 
result
    of the first call.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/mm.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 67c0427963..796faca641 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -887,7 +887,7 @@ get_page_from_l1e(
     uint32_t l1f = l1e_get_flags(l1e);
     struct vcpu *curr = current;
     struct domain *real_pg_owner;
-    bool write;
+    bool write, valid;
 
     if ( unlikely(!(l1f & _PAGE_PRESENT)) )
     {
@@ -902,13 +902,15 @@ get_page_from_l1e(
         return -EINVAL;
     }
 
-    if ( !mfn_valid(_mfn(mfn)) ||
+    valid = mfn_valid(_mfn(mfn));
+
+    if ( !valid ||
          (real_pg_owner = page_get_owner_and_reference(page)) == dom_io )
     {
         int flip = 0;
 
         /* Only needed the reference to confirm dom_io ownership. */
-        if ( mfn_valid(_mfn(mfn)) )
+        if ( valid )
             put_page(page);
 
         /* DOMID_IO reverts to caller for privilege checks. */
--
generated by git-patchbot for /home/xen/git/xen.git#staging