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Date: Mon, 8 Apr 2019 11:08:58 -0700
From: Thomas Garnier <>
To: Christopher Lameter <>
Cc: Kernel Hardening <>, 
	Kristen Carlson Accardi <>, Andy Lutomirski <>, 
	Thomas Gleixner <>, Ingo Molnar <>, Borislav Petkov <>, 
	"H. Peter Anvin" <>, "the arch/x86 maintainers" <>, Dennis Zhou <>, 
	Tejun Heo <>, Boris Ostrovsky <>, 
	Juergen Gross <>, Stefano Stabellini <>, 
	Andrew Morton <>, Andi Kleen <>, 
	"Kirill A. Shutemov" <>, Michal Hocko <>, 
	Mike Rapoport <>, Stephen Rothwell <>, 
	Cao jin <>, Brijesh Singh <>, 
	Masahiro Yamada <>, Joerg Roedel <>, 
	Peter Zijlstra <>, Kees Cook <>, 
	Mathieu Desnoyers <>, LKML <>, 
	xen-devel <>
Subject: Re: [PATCH v6 14/27] x86/percpu: Adapt percpu for PIE support

On Mon, Apr 8, 2019 at 10:56 AM Christopher Lameter <> wrote:
> On Mon, 8 Apr 2019, Thomas Garnier wrote:
> > > It didn't work originally but I will revisit to see if I missed something.
> >
> > I revisited and couldn't find a way to prevent relocations to the
> > percpu section. Without PIE, you can reference absolute address which
> > was convenient for percpu.
> Can you switch PIE off for the percpu section? If not maybe the linker
> needs to have an additional option?

I don't think so or I didn't find any option to do that. Changing the
linker might be a bit too much if we have a software solution which
doesn't impact performance.

> Cannot imagine that this is not possible. You neeed to be able to
> reference registers that are in fixed memory locations.
> > Christopher: Did you have something specific in mind?
> I thought that we just leave it as is.

I would like to as well. I will try couple things at the assembly
level instead of the linker and come back to this thread.

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