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Date: Fri, 26 Jan 2018 01:01:36 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: 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>,
	Andi Kleen <ak@linux.intel.com>,
	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>,
	Laura Abbott <labbott@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Radim Krcmar <rkrcmar@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Tom Lendacky <thomas.lendacky@amd.com>, X86 ML <x86@kernel.org>
Subject: Re: [RFC PATCH 1/2] x86/ibpb: Skip IBPB when we switch back to same
 user process
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On Thu, Jan 25, 2018 at 01:04:23PM -0800, Andy Lutomirski wrote:
> Can we please not rely on any of the active_mm shit?  That thing has
> really weird semantics and should just die.

I don't agree on the weird semantics. Its simply the last user mm.

I won't mind seeing it go as it would reduce the number of atomics on
the schedule path, but its really not terribly.