vmx: Do not disable real EFER.NXE even when disabled by guest.

We must not disable EFER.NXE in host mode since shadow code relies on
accessing shadow mappings with NX set.

We do not want to write EFER on every vmentry/vmexit if we can avoid
it, since it will be somewhat slow.

Finally, we don't believe that any guest relies on NX really being
disabled when EFER.NXE is cleared.

This given, it makes sense to ignore the guest's setting of EFER.NXE.

Signed-off-by: Keir Fraser <keir.fraser@citrix.com>
xen-unstable changeset:   18922:c3df4b8ea2fc2e86ecf4de97cf3f5516cac8eade
xen-unstable date:        Tue Dec 16 11:54:11 2008 +0000

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 88f93da6510b236f8000b1f96a665208c147b800..19ac0ac73bcb34041e555112fd8546d680de3b7f 100644 (file)
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -275,9 +275,6 @@ static void vmx_restore_host_msrs(void)
         wrmsrl(msr_index[i], host_msr_state->msrs[i]);
         clear_bit(i, &host_msr_state->flags);
     }
-
-    if ( cpu_has_nx && !(read_efer() & EFER_NX) )
-        write_efer(read_efer() | EFER_NX);
 }
 
 static void vmx_save_guest_msrs(struct vcpu *v)
@@ -311,39 +308,23 @@ static void vmx_restore_guest_msrs(struct vcpu *v)
         clear_bit(i, &guest_flags);
     }
 
-    if ( (v->arch.hvm_vcpu.guest_efer ^ read_efer()) & (EFER_NX | EFER_SCE) )
+    if ( (v->arch.hvm_vcpu.guest_efer ^ read_efer()) & EFER_SCE )
     {
         HVM_DBG_LOG(DBG_LEVEL_2,
                     "restore guest's EFER with value %lx",
                     v->arch.hvm_vcpu.guest_efer);
-        write_efer((read_efer() & ~(EFER_NX | EFER_SCE)) |
-                   (v->arch.hvm_vcpu.guest_efer & (EFER_NX | EFER_SCE)));
+        write_efer((read_efer() & ~EFER_SCE) |
+                   (v->arch.hvm_vcpu.guest_efer & EFER_SCE));
     }
 }
 
 #else  /* __i386__ */
 
 #define vmx_save_host_msrs()        ((void)0)
-
-static void vmx_restore_host_msrs(void)
-{
-    if ( cpu_has_nx && !(read_efer() & EFER_NX) )
-        write_efer(read_efer() | EFER_NX);
-}
+#define vmx_restore_host_msrs()     ((void)0)
 
 #define vmx_save_guest_msrs(v)      ((void)0)
-
-static void vmx_restore_guest_msrs(struct vcpu *v)
-{
-    if ( (v->arch.hvm_vcpu.guest_efer ^ read_efer()) & EFER_NX )
-    {
-        HVM_DBG_LOG(DBG_LEVEL_2,
-                    "restore guest's EFER with value %lx",
-                    v->arch.hvm_vcpu.guest_efer);
-        write_efer((read_efer() & ~EFER_NX) |
-                   (v->arch.hvm_vcpu.guest_efer & EFER_NX));
-    }
-}
+#define vmx_restore_guest_msrs(v)   ((void)0)
 
 static enum handler_return long_mode_do_msr_read(struct cpu_user_regs *regs)
 {
@@ -1115,8 +1096,8 @@ static void vmx_update_guest_efer(struct vcpu *v)
 #endif
 
     if ( v == current )
-        write_efer((read_efer() & ~(EFER_NX|EFER_SCE)) |
-                   (v->arch.hvm_vcpu.guest_efer & (EFER_NX|EFER_SCE)));
+        write_efer((read_efer() & ~EFER_SCE) |
+                   (v->arch.hvm_vcpu.guest_efer & EFER_SCE));
 }
 
 static void vmx_flush_guest_tlbs(void)