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From: Andi Kleen <ak@linux.intel.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: 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>
Subject: Re: [RFC PATCH 1/2] x86/ibpb: Skip IBPB when we switch back to same user process
References: <c5cc429013c2248ddebe0a8480b172ae70b29733.1516840211.git.tim.c.chen@linux.intel.com>
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Date: Thu, 25 Jan 2018 13:57:49 -0800
In-Reply-To: <CALCETrUGDeHse24sOygh5EcsXuZHPtZnw3adhzADfn+yKgcOzg@mail.gmail.com>
	(Andy Lutomirski's message of "Thu, 25 Jan 2018 13:04:23 -0800")
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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.

-Andi