[Xen-changelog] [xen-unstable] x86 vmx: Streamline vmx_interrupt_blocked() to avoid a VMREAD if

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

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1202920118 0
# Node ID 4c64376d439d3237e81f56b0fdfac7fe6601ec82
# Parent  e56c9fe4a7e6d044d31a052072e6bfb06ee58535
x86 vmx: Streamline vmx_interrupt_blocked() to avoid a VMREAD if
interrupt delivery is blocked by EFLAGS.IF. This speeds up real-mode
emulation in some cases (where we are currently executing
hvm_local_events_need_delivery() after every instruction).
Signed-off-by: Keir Fraser <keir.fraser@xxxxxxxxxx>
---
 xen/arch/x86/hvm/vmx/vmx.c |   11 ++++++++---
 1 files changed, 8 insertions(+), 3 deletions(-)

diff -r e56c9fe4a7e6 -r 4c64376d439d xen/arch/x86/hvm/vmx/vmx.c
--- a/xen/arch/x86/hvm/vmx/vmx.c        Wed Feb 13 16:25:32 2008 +0000
+++ b/xen/arch/x86/hvm/vmx/vmx.c        Wed Feb 13 16:28:38 2008 +0000
@@ -917,6 +917,14 @@ static enum hvm_intblk vmx_interrupt_blo
 {
     unsigned long intr_shadow;
 
+    /*
+     * Test EFLAGS.IF first. It is often the most likely reason for interrupt
+     * blockage, and is the cheapest to test (because no VMREAD is required).
+     */
+    if ( (intack.source != hvm_intsrc_nmi) &&
+         !(guest_cpu_user_regs()->eflags & X86_EFLAGS_IF) )
+        return hvm_intblk_rflags_ie;
+
     intr_shadow = __vmread(GUEST_INTERRUPTIBILITY_INFO);
 
     if ( intr_shadow & (VMX_INTR_SHADOW_STI|VMX_INTR_SHADOW_MOV_SS) )
@@ -928,9 +936,6 @@ static enum hvm_intblk vmx_interrupt_blo
 
     ASSERT((intack.source == hvm_intsrc_pic) ||
            (intack.source == hvm_intsrc_lapic));
-
-    if ( !(guest_cpu_user_regs()->eflags & X86_EFLAGS_IF) )
-        return hvm_intblk_rflags_ie;
 
     return hvm_intblk_none;
 }

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