linux-kernel - Re: cpu_no_speculation omissions?

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Message-ID: <20180716195444.GN1392@brightrain.aerifal.cx>
Date:   Mon, 16 Jul 2018 15:54:44 -0400
From:   Rich Felker <dalias@...c.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Alan Cox <alan@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: cpu_no_speculation omissions?

On Mon, Jul 16, 2018 at 09:20:58PM +0200, Thomas Gleixner wrote:
> On Mon, 16 Jul 2018, Alan Cox wrote:
> > On Mon, 2018-07-16 at 10:28 -0700, Dave Hansen wrote:
> > > On 07/16/2018 09:56 AM, Thomas Gleixner wrote:
> > > > On Mon, 16 Jul 2018, Rich Felker wrote:
> > > > > At least the Centerton (late-generation Bonnell uarch) Atom
> > > > > family is
> > > > > omitted from the cpu_no_speculation table added by commit
> > > > > fec9434a12f3
> > > > > to arch/x86/kernel/cpu/common.c. Is this intentional? Would a
> > > > > patch
> > > > > adding it and possibly other omissions be welcome?
> > > > 
> > > > Probably. Dave?
> > > 
> > > IIRC, Alan Cox was compiling a list on what is affected vs. not.  He
> > > would know way better than I.
> > 
> > The pre Silvermont atom cores are in order. When I did the original
> > list I didn't bother with all the 32bit cores as we didn't have any
> > 32bit mitigations then.
> 
> At least we should give the users that warm and fuzzy feeling that they are
> not affected.

It's not just fuzzies -- my box was actually affected by slowdown for
mitigation without adding "nopti" to boot command line, which is
rather unfortunate when you're running a severely-slower box already
for the sake of not being affected by these vulnerabilities.

Since Dave asked, mine is a Centerton as I originally mentioned, Atom
S1260, which seems to be the fastest in-order Intel chip with boards
still commercially available. I'm not sure if there are other
omissions that are actually interesting. I have several other Atoms
too, but I think all of those are covered by the existing table.

Rich