[Xen-devel] [PATCH v2 1/3] x86/mm: mod_l<N>_entry() have no need to use __copy_from_user()

[Jan Beulich <jbeulich@xxxxxxxx>]

mod_l1_entry()'s need to do so went away with commit 2d0557c5cb ("x86:
Fold page_info lock into type_info"), and the other three never had such
a need, at least going back as far as 3.2.0. Replace the uses by newly
introduced l<N>e_access_once().

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: Use ACCESS_ONCE() clones.

--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -2124,13 +2124,10 @@ static int mod_l1_entry(l1_pgentry_t *pl
                         struct vcpu *pt_vcpu, struct domain *pg_dom)
 {
     bool preserve_ad = (cmd == MMU_PT_UPDATE_PRESERVE_AD);
-    l1_pgentry_t ol1e;
+    l1_pgentry_t ol1e = l1e_access_once(*pl1e);
     struct domain *pt_dom = pt_vcpu->domain;
     int rc = 0;
 
-    if ( unlikely(__copy_from_user(&ol1e, pl1e, sizeof(ol1e)) != 0) )
-        return -EFAULT;
-
     ASSERT(!paging_mode_refcounts(pt_dom));
 
     if ( l1e_get_flags(nl1e) & _PAGE_PRESENT )
@@ -2248,8 +2245,7 @@ static int mod_l2_entry(l2_pgentry_t *pl
         return -EPERM;
     }
 
-    if ( unlikely(__copy_from_user(&ol2e, pl2e, sizeof(ol2e)) != 0) )
-        return -EFAULT;
+    ol2e = l2e_access_once(*pl2e);
 
     if ( l2e_get_flags(nl2e) & _PAGE_PRESENT )
     {
@@ -2311,8 +2307,7 @@ static int mod_l3_entry(l3_pgentry_t *pl
     if ( is_pv_32bit_domain(d) && (pgentry_ptr_to_slot(pl3e) >= 3) )
         return -EINVAL;
 
-    if ( unlikely(__copy_from_user(&ol3e, pl3e, sizeof(ol3e)) != 0) )
-        return -EFAULT;
+    ol3e = l3e_access_once(*pl3e);
 
     if ( l3e_get_flags(nl3e) & _PAGE_PRESENT )
     {
@@ -2378,8 +2373,7 @@ static int mod_l4_entry(l4_pgentry_t *pl
         return -EINVAL;
     }
 
-    if ( unlikely(__copy_from_user(&ol4e, pl4e, sizeof(ol4e)) != 0) )
-        return -EFAULT;
+    ol4e = l4e_access_once(*pl4e);
 
     if ( l4e_get_flags(nl4e) & _PAGE_PRESENT )
     {
--- a/xen/include/asm-x86/page.h
+++ b/xen/include/asm-x86/page.h
@@ -55,6 +55,16 @@
 #define l4e_write(l4ep, l4e) \
     pte_write(&l4e_get_intpte(*(l4ep)), l4e_get_intpte(l4e))
 
+/* Type-correct ACCESS_ONCE() wrappers for PTE accesses. */
+#define l1e_access_once(l1e) (*container_of(&ACCESS_ONCE(l1e_get_intpte(l1e)), 
\
+                                            volatile l1_pgentry_t, l1))
+#define l2e_access_once(l2e) (*container_of(&ACCESS_ONCE(l2e_get_intpte(l2e)), 
\
+                                            volatile l2_pgentry_t, l2))
+#define l3e_access_once(l3e) (*container_of(&ACCESS_ONCE(l3e_get_intpte(l3e)), 
\
+                                            volatile l3_pgentry_t, l3))
+#define l4e_access_once(l4e) (*container_of(&ACCESS_ONCE(l4e_get_intpte(l4e)), 
\
+                                            volatile l4_pgentry_t, l4))
+
 /* Get direct integer representation of a pte's contents (intpte_t). */
 #define l1e_get_intpte(x)          ((x).l1)
 #define l2e_get_intpte(x)          ((x).l2)


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