Re: [patch] i386: remove IOPL check on task switch

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Chuck Ebbert wrote:
IOPL is implicitly saved and restored on task switch,
so explicit check is no longer needed.

Signed-off-by: Chuck Ebbert <[email protected]>

--- 2.6.19-rc4-32smp.orig/arch/i386/kernel/process.c
+++ 2.6.19-rc4-32smp/arch/i386/kernel/process.c
@@ -681,12 +681,6 @@ struct task_struct fastcall * __switch_t
 		loadsegment(gs, next->gs);
/*
-	 * Restore IOPL if needed.
-	 */
-	if (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)

Nack. This is used for paravirt-ops kernels that use IOPL'd userspace. Fixing it would require a fairly heavy penalty on the iret path, since every single instruction there contributes to a critical region which must have custom fixup code, or some other technique to provide protection against interrupt re-entrancy.

At least, let's discuss other potential solutions first - for now it is harmless.

Zach
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