linux-kernel - Re: [PATCH 0/2] Backport IBPB on context switch to non-dumpable process

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Date:   Sat, 3 Mar 2018 09:54:54 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     stable@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Nadav Amit <nadav.amit@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Rik van Riel <riel@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        David Woodhouse <dwmw@...zon.co.uk>, ak@...ux.intel.com,
        karahmed@...zon.de, pbonzini@...hat.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Backport IBPB on context switch to non-dumpable
 process

On Fri, Mar 02, 2018 at 01:32:08PM -0800, Tim Chen wrote:
> Greg,
> 
> I will like to propose backporting "x86/speculation: Use Indirect Branch
> Prediction Barrier on context switch" from commit 18bf3c3e in upstream
> to 4.9 and 4.4 stable.  The patch has already been ported to 4.14 and
> 4.15 stable.  The patch needs mm context id that Andy added in commit
> f39681ed. I have lifted the mm context id change from Andy's upstream
> patch and included it here.

What does this patch "fix" in those older kernels?  Is this a
performance improvement or something else?

thanks,

greg k-h