[xen staging] x86/PV: use get_unsafe() instead of copy_from_unsafe()

[patchbot@xxxxxxx]

commit 972cd4308775f4eb48cbba3cc4efaf39e55c8057
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Feb 25 15:39:09 2021 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Feb 25 15:39:09 2021 +0100

    x86/PV: use get_unsafe() instead of copy_from_unsafe()
    
    The former expands to a single (memory accessing) insn, which the latter
    does not guarantee (the __builtin_constant_p() based switch() statement
    there is just an optimization). Yet we'd prefer to read consistent PTEs
    rather than risking a split read racing with an update done elsewhere.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Release-Acked-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>
---
 xen/arch/x86/pv/mm.c | 4 +---
 xen/arch/x86/pv/mm.h | 4 +---
 2 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/pv/mm.c b/xen/arch/x86/pv/mm.c
index cb86143832..5ed7b3ccdb 100644
--- a/xen/arch/x86/pv/mm.c
+++ b/xen/arch/x86/pv/mm.c
@@ -41,9 +41,7 @@ l1_pgentry_t *map_guest_l1e(unsigned long linear, mfn_t 
*gl1mfn)
         return NULL;
 
     /* Find this l1e and its enclosing l1mfn in the linear map. */
-    if ( copy_from_unsafe(&l2e,
-                          &__linear_l2_table[l2_linear_offset(linear)],
-                          sizeof(l2_pgentry_t)) )
+    if ( get_unsafe(l2e, &__linear_l2_table[l2_linear_offset(linear)]) )
         return NULL;
 
     /* Check flags that it will be safe to read the l1e. */
diff --git a/xen/arch/x86/pv/mm.h b/xen/arch/x86/pv/mm.h
index 7e2259c488..5a117c735d 100644
--- a/xen/arch/x86/pv/mm.h
+++ b/xen/arch/x86/pv/mm.h
@@ -22,9 +22,7 @@ static inline l1_pgentry_t guest_get_eff_kern_l1e(unsigned 
long linear)
         toggle_guest_pt(curr);
 
     if ( unlikely(!__addr_ok(linear)) ||
-         copy_from_unsafe(&l1e,
-                          &__linear_l1_table[l1_linear_offset(linear)],
-                          sizeof(l1_pgentry_t)) )
+         get_unsafe(l1e, &__linear_l1_table[l1_linear_offset(linear)]) )
         l1e = l1e_empty();
 
     if ( user_mode )
--
generated by git-patchbot for /home/xen/git/xen.git#staging