[Patch 1/3 v2] x86/irq: local_irq_restore() should not blindly popf

[Andrew Cooper <andrew.cooper3@citrix.com>]

local_irq_restore() should only be concerned with possibly changing the
interrupt flag.  A blind popf could corrupt other system flags.

While playing in this area, fixup an opencoded use of X86_EFLAGS_IF.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Keir Fraser <keir@xen.org>
CC: Jan Beulich <JBeulich@suse.com>

---

This is rather more RFC.  It boots and runs VMs, so I am fairly sure it is
functionally correct, but I cant help feeling there might be a neater way to
do the inline assembly.  Suggestions welcome.
---
 xen/include/asm-x86/system.h |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/xen/include/asm-x86/system.h b/xen/include/asm-x86/system.h
index 6ab7d56..ff52671 100644
--- a/xen/include/asm-x86/system.h
+++ b/xen/include/asm-x86/system.h
@@ -3,6 +3,7 @@
 
 #include <xen/lib.h>
 #include <xen/bitops.h>
+#include <asm/processor.h>
 
 #define read_segment_register(name)                             \
 ({  u16 __sel;                                                  \
@@ -159,15 +160,19 @@ static always_inline unsigned long __cmpxchg(
 #define local_irq_restore(x)                                     \
 ({                                                               \
     BUILD_BUG_ON(sizeof(x) != sizeof(long));                     \
-    asm volatile ( "push" __OS " %0 ; popf" __OS                 \
-                   : : "g" (x) : "memory", "cc" );               \
+    asm volatile (                                               \
+    "pushf" __OS "\n\t"                                          \
+    "and" __OS " %0, (%%" __OP "sp)\n\t"                         \
+    "orw %1, (%%" __OP "sp)\n\t"                                 \
+    "popf" __OS "\n\t" : : "g" ( ~X86_EFLAGS_IF ),               \
+                           "g" ( x & X86_EFLAGS_IF ) );          \
 })
 
 static inline int local_irq_is_enabled(void)
 {
     unsigned long flags;
     local_save_flags(flags);
-    return !!(flags & (1<<9)); /* EFLAGS_IF */
+    return !!(flags & X86_EFLAGS_IF);
 }
 
 #define BROKEN_ACPI_Sx          0x0001
-- 
1.7.10.4