From: Zachary Amsden <[email protected]>
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.
Signed-off-by: Zachary Amsden <[email protected]>
Signed-off-by: Andi Kleen <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Jeremy Fitzhardinge <[email protected]>
Cc: Rusty Russell <[email protected]>
Cc: Chris Wright <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---
arch/i386/kernel/process.c | 9 +++++++++
1 file changed, 9 insertions(+)
Index: linux/arch/i386/kernel/process.c
===================================================================
--- linux.orig/arch/i386/kernel/process.c
+++ linux/arch/i386/kernel/process.c
@@ -670,6 +670,15 @@ 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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