Implement direct iret to guest kernel where possible in HYPERVISOR_IRET macro.

Returns to guest userspace and from an NMI must still go via the hypervisor.

Signed-off-by: Ian Campbell <ian.campbell@xensource.com>

diff --git a/linux-2.6-xen-sparse/arch/x86_64/kernel/entry-xen.S b/linux-2.6-xen-sparse/arch/x86_64/kernel/entry-xen.S
index c2733797b3e0684712b2730789d2059296cc636e..6a8e1c0a9f49b56519e65c8692e73e71a1419049 100644 (file)
--- a/linux-2.6-xen-sparse/arch/x86_64/kernel/entry-xen.S
+++ b/linux-2.6-xen-sparse/arch/x86_64/kernel/entry-xen.S
@@ -61,6 +61,8 @@
 #ifndef CONFIG_PREEMPT
 #define retint_kernel retint_restore_args
 #endif 
+
+NMI_MASK = 0x80000000
        
 /*
  * C code is not supposed to know about undefined top of stack. Every time 
@@ -143,6 +145,18 @@
          * #define VGCF_IN_SYSCALL (1<<8) 
          */
        .macro HYPERVISOR_IRET flag
+       testb $3,1*8(%rsp)
+       jnz   1f
+       testl $NMI_MASK,2*8(%rsp)
+       jnz   1f
+
+       /* Direct iret to kernel space. Correct CS and SS. */
+       orb   $3,1*8(%rsp)
+       orb   $3,4*8(%rsp)
+       iretq
+
+1:     /* Slow iret via hypervisor. */
+       andl  $~NMI_MASK, 16(%rsp)
        pushq $\flag
        jmp  hypercall_page + (__HYPERVISOR_iret * 32)
        .endm
@@ -805,6 +819,7 @@ ENTRY(nmi)
 ENTRY(do_nmi_callback)
         addq $8, %rsp
         call do_nmi
+        orl  $NMI_MASK,EFLAGS(%rsp)
         RESTORE_REST
         XEN_BLOCK_EVENTS(%rsi)
         GET_THREAD_INFO(%rcx)