[Xen-changelog] [xen-unstable] vmx: Do not disable real EFER.NXE even when disabled by guest.

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1229428451 0
# Node ID c3df4b8ea2fc2e86ecf4de97cf3f5516cac8eade
# Parent  5b73fa1b9562d18ecdde2b3c8556989bdb2117e0
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@xxxxxxxxxx>
---
 xen/arch/x86/hvm/vmx/vmx.c |   33 +++++++--------------------------
 1 files changed, 7 insertions(+), 26 deletions(-)

diff -r 5b73fa1b9562 -r c3df4b8ea2fc xen/arch/x86/hvm/vmx/vmx.c
--- a/xen/arch/x86/hvm/vmx/vmx.c        Tue Dec 16 11:49:20 2008 +0000
+++ b/xen/arch/x86/hvm/vmx/vmx.c        Tue Dec 16 11:54:11 2008 +0000
@@ -306,9 +306,6 @@ 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)
@@ -342,39 +339,23 @@ static void vmx_restore_guest_msrs(struc
         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)
 {
@@ -1190,8 +1171,8 @@ static void vmx_update_guest_efer(struct
 #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)

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