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Subject: Re: [RFC PATCH 1/2] x86/ibpb: Skip IBPB when we switch back to same
 user process
To: Andy Lutomirski <luto@kernel.org>, Andi Kleen <ak@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
 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>
References: <c5cc429013c2248ddebe0a8480b172ae70b29733.1516840211.git.tim.c.chen@linux.intel.com>
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From: Tim Chen <tim.c.chen@linux.intel.com>
Message-ID: <f232ce18-3122-b045-be92-76fd61b195b5@linux.intel.com>
Date: Thu, 25 Jan 2018 15:07:11 -0800
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On 01/25/2018 02:01 PM, Andy Lutomirski wrote:
> 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
> 
Thanks.  Using ctx_id is a pretty clean approach.  I will refresh
this patch and drop the second patch.

Tim