linux-kernel - Re: Improve retpoline for Skylake

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Message-ID: <20180112192126.su2evwfefdfeaa6g@two.firstfloor.org>
Date:   Fri, 12 Jan 2018 11:21:26 -0800
From:   Andi Kleen <andi@...stfloor.org>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     Andi Kleen <andi@...stfloor.org>, tglx@...utronix.de,
        x86@...nel.org, linux-kernel@...r.kernel.org, pjt@...gle.com,
        torvalds@...ux-foundation.org, gregkh@...ux-foundation.org,
        peterz@...radead.org, luto@...capital.net, thomas.lendacky@....com,
        arjan.van.de.ven@...el.com
Subject: Re: Improve retpoline for Skylake

> 
> Skylake still loses if it takes an SMI, right? 

SMMs are usually rare, especially on servers, and are usually
not very predictible, and even if you have
one it would need to interrupt on a quite narrow window, so difficult
to arrange. I don't worry about SMM.

> Or encounters a call
> stack of more than 16 in depth?

Yes that's it. This could be mitigated over time.

-Andi