xen: mask unwanted pte bits in __supported_pte_mask

[ Stable: this isn't a bugfix in itself, but it's a pre-requiste
  for "xen: don't drop NX bit" ]

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Stable Kernel <stable@kernel.org>
Cc: the arch/x86 maintainers <x86@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 6 insertions, 3 deletions

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index c8a56e457d61..c048de34d6a1 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1228,6 +1228,11 @@ asmlinkage void __init xen_start_kernel(void)
         if (xen_feature(XENFEAT_supervisor_mode_kernel))
                 pv_info.kernel_rpl = 0;
 
+        /* Prevent unwanted bits from being set in PTEs. */
+        __supported_pte_mask &= ~_PAGE_GLOBAL;
+        if (!is_initial_xendomain())
+                __supported_pte_mask &= ~(_PAGE_PWT | _PAGE_PCD);
+
         /* set the limit of our address space */
         xen_reserve_top();
 
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index 3525ef523a74..3f2a67fe6ad6 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -199,10 +199,8 @@ pgdval_t xen_pgd_val(pgd_t pgd)
 
 pte_t xen_make_pte(pteval_t pte)
 {
-        if (pte & _PAGE_PRESENT) {
+        if (pte & _PAGE_PRESENT)
                 pte = phys_to_machine(XPADDR(pte)).maddr;
-                pte &= ~(_PAGE_PCD | _PAGE_PWT);
-        }
 
         return (pte_t){ .pte = pte };
 }