linux-kernel - Re: [RFC PATCH 1/2] x86/ibpb: Skip IBPB when we switch back to same user process

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Message-ID: <87h8r9k3du.fsf@linux.intel.com>
Date:   Thu, 25 Jan 2018 13:57:49 -0800
From:   Andi Kleen <ak@...ux.intel.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        KarimAllah Ahmed <karahmed@...zon.de>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Borislav Petkov <bp@...e.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Janakarajan Natarajan <Janakarajan.Natarajan@....com>,
        Joerg Roedel <joro@...tes.org>,
        Jun Nakajima <jun.nakajima@...el.com>
Subject: Re: [RFC PATCH 1/2] x86/ibpb: Skip IBPB when we switch back to same user process

Andy Lutomirski <luto@...nel.org> writes:
>
> That being said, just stashing last_user_mm without any refcounting
> should be fine.

If last_user_mm is freed and reallocated by a different process,
then that would miss the IPBP incorrectly.

-Andi