linux-kernel - [RFC 0/5] CR4 handling improvements

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Date:	Tue, 14 Oct 2014 15:57:34 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Kees Cook <keescook@...omium.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Erik Bosman <ebn310@....vu.nl>,
	Andy Lutomirski <luto@...capital.net>
Subject: [RFC 0/5] CR4 handling improvements

Hi Peter, etc,

This little series tightens up rdpmc permissions.  With it applied,
rdpmc can only be used if a perf_event is actually mmapped.  For now,
this is only really useful for seccomp.

At some point this could be further tightened up to only allow rdpmc
if an actual self-monitoring perf event that is compatible with
rdpmc is mapped.  (Is the current code there even correct?  What
happens if you set up a perf counter targetting a different pid and
then try to rdpmc it?  Do you end up reading the right value or does
perf event context switching mess you up?)

This should add <50ns to context switches between rdpmc-capable and
rdpmc-non-capable mms.  I suspect that this is well under 10%
overhead, given that perf already adds some context switch latency.

If needed, we could add a global switch that turns this behavior
off.  We could also rehink the logic.

I think that patches 1-3 are a good idea regardless of any rdpmc changes.

(Please don't apply quite yet, because there'll be a merge conflict
with some changes that haven't landed yet.  This is against 3.17.)

Andy Lutomirski (5):
  x86: Clean up cr4 manipulation
  x86: Store a per-cpu shadow copy of CR4
  x86: Add a comment clarifying LDT context switching
  perf: Add pmu callbacks to track event mapping and unmapping
  x86,perf: Only allow rdpmc if a perf_event is mapped

 arch/x86/include/asm/mmu.h           |  2 +
 arch/x86/include/asm/mmu_context.h   | 30 +++++++++++++-
 arch/x86/include/asm/processor.h     | 33 ----------------
 arch/x86/include/asm/tlbflush.h      | 77 ++++++++++++++++++++++++++++++++----
 arch/x86/include/asm/virtext.h       |  3 +-
 arch/x86/kernel/cpu/common.c         | 17 +++++---
 arch/x86/kernel/cpu/mcheck/mce.c     |  3 +-
 arch/x86/kernel/cpu/mcheck/p5.c      |  3 +-
 arch/x86/kernel/cpu/mcheck/winchip.c |  3 +-
 arch/x86/kernel/cpu/perf_event.c     | 61 +++++++++++++++++++++-------
 arch/x86/kernel/head32.c             |  1 +
 arch/x86/kernel/head64.c             |  2 +
 arch/x86/kernel/i387.c               |  3 +-
 arch/x86/kernel/process.c            |  5 ++-
 arch/x86/kernel/xsave.c              |  3 +-
 arch/x86/kvm/vmx.c                   |  8 ++--
 arch/x86/mm/init.c                   | 12 +++++-
 arch/x86/mm/tlb.c                    |  3 --
 arch/x86/xen/enlighten.c             |  4 +-
 include/linux/perf_event.h           |  7 ++++
 kernel/events/core.c                 |  9 +++++
 21 files changed, 210 insertions(+), 79 deletions(-)

-- 
1.9.3

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