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

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Message-ID: <20181121181513.GA30870@kroah.com>
Date:   Wed, 21 Nov 2018 19:15:13 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     Jiri Kosina <jikos@...nel.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, Nov 21, 2018 at 09:47:48AM -0800, Tim Chen wrote:
> On 11/21/2018 05:56 AM, Greg Kroah-Hartman wrote:
> > On Wed, Nov 21, 2018 at 02:21:15PM +0100, Jiri Kosina wrote:
> >> On Sun, 11 Nov 2018, Greg Kroah-Hartman wrote:
> >>
> >>> 4.19-stable review patch.  If anyone has any objections, please let me know.
> >>
> >> Greg, please drop this patch from all -stable for now. Version that 
> >> wouldn't have such performance impact is being worked on.
> > 
> > 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.

Ok, now reverted, thanks.

greg k-h