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From:   Andy Lutomirski <luto@kernel.org>
Date:   Thu, 25 Jan 2018 14:01:27 -0800
Message-ID: <CALCETrVnMT+hTL+U2s6Axhr3KmJY+L+czpkbmQd3qytB6FHnGw@mail.gmail.com>
Subject: Re: [RFC PATCH 1/2] x86/ibpb: Skip IBPB when we switch back to same
 user process
To:     Andi Kleen <ak@linux.intel.com>
Cc:     Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Arjan van de Ven <arjan@linux.intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        KarimAllah Ahmed <karahmed@amazon.de>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Asit Mallick <asit.k.mallick@intel.com>,
        Borislav Petkov <bp@suse.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        David Woodhouse <dwmw@amazon.co.uk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "H . Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>,
        Joerg Roedel <joro@8bytes.org>,
        Jun Nakajima <jun.nakajima@intel.com>
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On Thu, Jan 25, 2018 at 1:57 PM, Andi Kleen <ak@linux.intel.com> wrote:
> Andy Lutomirski <luto@kernel.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.
>

Hmm, right.  So ctx_id it is.

--Andy