linux-kernel - Re: [PATCH v2] x86: Disable kernel stack offset randomization for !TSC

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Message-ID: <alpine.DEB.2.21.2301302034340.55843@angie.orcam.me.uk>
Date:   Mon, 30 Jan 2023 20:43:47 +0000 (GMT)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] x86: Disable kernel stack offset randomization for
 !TSC

Hi Jason,

> >  Thank you for your input.  I've had a look at the function and it seems a
> > bit heavyweight compared to a mere single CPU instruction, but I guess why
> > not.  Do you have any performance figures (in terms of CPU cycles) for the
> > usual cases?  Offhand I'm not sure how I could benchmark it myself.
> 
> Generally it's very very fast, as most cases wind up being only a
> memcpy -- in this case, a single byte copy. So by and large it should
> be suitable. It's fast enough now that most networking things are able
> to use it. And lots of other places where you'd want really high
> performance. So I'd expect it's okay to use here too. And if it is too
> slow, we should figure out how to make it faster. But I don't suspect
> it'll be too slow.

 Thank you for your explanation.  I have v3 ready for submission; would 
you mind if I added you with a Suggested-by: tag?

  Maciej