Re: [PATCH] x86: entry_32.S: change ESPFIX test to not touch PT_OLDSS(%esp)

From: H. Peter Anvin
Date: Mon Mar 09 2015 - 13:44:58 EST

On 03/09/2015 09:44 AM, Linus Torvalds wrote:
> And remember: those zero-cost out-of-order branches turn quite
> expensive if they *ever* mispredict. Even a 5% mispredict rate is
> likely to mean "it's better to have a data dependency chain".
> So it could easily go either way. I'm not convinced the old code is bad at all.

I'm inclined to side with Linus here. I'm hesitant to change this based
on pure speculation.

To answer Andy's question: I do believe we need espfix for V86 mode as well.


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