patches/kernel/0303-x86-perf-Disable-intel_bts-when-PTI.patch

   1 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
   2 From: Peter Zijlstra <peterz@infradead.org>
   3 Date: Sun, 14 Jan 2018 11:27:13 +0100
   4 Subject: [PATCH] x86,perf: Disable intel_bts when PTI
   5 MIME-Version: 1.0
   6 Content-Type: text/plain; charset=UTF-8
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   8
   9 commit 99a9dc98ba52267ce5e062b52de88ea1f1b2a7d8 upstream.
  10
  11 The intel_bts driver does not use the 'normal' BTS buffer which is exposed
  12 through the cpu_entry_area but instead uses the memory allocated for the
  13 perf AUX buffer.
  14
  15 This obviously comes apart when using PTI because then the kernel mapping;
  16 which includes that AUX buffer memory; disappears. Fixing this requires to
  17 expose a mapping which is visible in all context and that's not trivial.
  18
  19 As a quick fix disable this driver when PTI is enabled to prevent
  20 malfunction.
  21
  22 Fixes: 385ce0ea4c07 ("x86/mm/pti: Add Kconfig")
  23 Reported-by: Vince Weaver <vincent.weaver@maine.edu>
  24 Reported-by: Robert Święcki <robert@swiecki.net>
  25 Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
  26 Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
  27 Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
  28 Cc: greg@kroah.com
  29 Cc: hughd@google.com
  30 Cc: luto@amacapital.net
  31 Cc: Vince Weaver <vince@deater.net>
  32 Cc: torvalds@linux-foundation.org
  33 Cc: stable@vger.kernel.org
  34 Link: https://lkml.kernel.org/r/20180114102713.GB6166@worktop.programming.kicks-ass.net
  35 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  36 Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
  37 ---
  38  arch/x86/events/intel/bts.c | 18 ++++++++++++++++++
  39  1 file changed, 18 insertions(+)
  40
  41 diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c
  42 index ddd8d3516bfc..9a62e6fce0e0 100644
  43 --- a/arch/x86/events/intel/bts.c
  44 +++ b/arch/x86/events/intel/bts.c
  45 @@ -582,6 +582,24 @@ static __init int bts_init(void)
  46         if (!boot_cpu_has(X86_FEATURE_DTES64) || !x86_pmu.bts)
  47                 return -ENODEV;
  48
  49 +       if (boot_cpu_has(X86_FEATURE_PTI)) {
  50 +               /*
  51 +                * BTS hardware writes through a virtual memory map we must
  52 +                * either use the kernel physical map, or the user mapping of
  53 +                * the AUX buffer.
  54 +                *
  55 +                * However, since this driver supports per-CPU and per-task inherit
  56 +                * we cannot use the user mapping since it will not be availble
  57 +                * if we're not running the owning process.
  58 +                *
  59 +                * With PTI we can't use the kernal map either, because its not
  60 +                * there when we run userspace.
  61 +                *
  62 +                * For now, disable this driver when using PTI.
  63 +                */
  64 +               return -ENODEV;
  65 +       }
  66 +
  67         bts_pmu.capabilities    = PERF_PMU_CAP_AUX_NO_SG | PERF_PMU_CAP_ITRACE |
  68                                   PERF_PMU_CAP_EXCLUSIVE;
  69         bts_pmu.task_ctx_nr     = perf_sw_context;
  70 --
  71 2.14.2
  72