linux-kernel - Re: [PATCH 4.19 041/361] x86/speculation: Enable cross-hyperthread spectre v2 STIBP mitigation

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Message-ID: <nycvar.YFH.7.76.1811211920570.21108@cbobk.fhfr.pm>
Date:   Wed, 21 Nov 2018 19:21:31 +0100 (CET)
From:   Jiri Kosina <jikos@...nel.org>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        WoodhouseDavid <dwmw@...zon.co.uk>,
        Andi Kleen <ak@...ux.intel.com>,
        SchauflerCasey <casey.schaufler@...el.com>,
        Dave Stewart <david.c.stewart@...el.com>
Subject: Re: [PATCH 4.19 041/361] x86/speculation: Enable cross-hyperthread
 spectre v2 STIBP mitigation

On Wed, 21 Nov 2018, Tim Chen wrote:

> > Is it reverted in Linus's tree?  If not, then anything that comes "later
> > on" will not apply here, right?
> > 
> > I see the thread asking about this, but I got really conflicting
> > messages here, and now it's in all of the latest releases, and no
> > testing seems to have uncovered issues.  Is it just a "slow down"
> > problem?
> 
> Greg,
> 
> It could be a big slow down in excess of 20% for some applications.
> And cross sibling Spectre v2 attack is quite hard to pull off.
> 
> So till we have the accompanying patchset that only apply STIBP on processes
> that really need it instead of universally, it should be withheld from
> stable.

Agreed; it will be trivially reintroduced with the rest, once it's ready. 
It's being built on top of that patch.

Thanks,

-- 
Jiri Kosina
SUSE Labs