I found a clever way to make the extra IOPL switching invisible to
non-paravirt compiles - since kernel_rpl is statically defined to
be zero there, and only non-zero rpl kernel have a problem restoring IOPL,
as popf does not restore IOPL flags unless run at CPL-0.

Subject: IOPL handling for paravirt guests
Signed-off-by: Zachary Amsden <[EMAIL PROTECTED]>

diff -r 8110943fd7ad arch/i386/kernel/process.c
--- a/arch/i386/kernel/process.c        Thu Dec 14 16:15:20 2006 -0800
+++ b/arch/i386/kernel/process.c        Thu Dec 14 16:21:57 2006 -0800
@@ -665,6 +665,15 @@ struct task_struct fastcall * __switch_t
        load_TLS(next, cpu);
 
        /*
+        * Restore IOPL if needed.  In normal use, the flags restore
+        * in the switch assembly will handle this.  But if the kernel
+        * is running virtualized at a non-zero CPL, the popf will
+        * not restore flags, so it must be done in a separate step.
+        */
+       if (get_kernel_rpl() && unlikely(prev->iopl != next->iopl))
+               set_iopl_mask(next->iopl);
+
+       /*
         * Now maybe handle debug registers and/or IO bitmaps
         */
        if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW)
-
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