queue-4.4/x86-speculation-rework-smt-state-change.patch

   1 From foo@baz Tue 14 May 2019 08:29:35 PM CEST
   2 From: Thomas Gleixner <tglx@linutronix.de>
   3 Date: Sun, 25 Nov 2018 19:33:39 +0100
   4 Subject: x86/speculation: Rework SMT state change
   5
   6 From: Thomas Gleixner <tglx@linutronix.de>
   7
   8 commit a74cfffb03b73d41e08f84c2e5c87dec0ce3db9f upstream.
   9
  10 arch_smt_update() is only called when the sysfs SMT control knob is
  11 changed. This means that when SMT is enabled in the sysfs control knob the
  12 system is considered to have SMT active even if all siblings are offline.
  13
  14 To allow finegrained control of the speculation mitigations, the actual SMT
  15 state is more interesting than the fact that siblings could be enabled.
  16
  17 Rework the code, so arch_smt_update() is invoked from each individual CPU
  18 hotplug function, and simplify the update function while at it.
  19
  20 Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
  21 Reviewed-by: Ingo Molnar <mingo@kernel.org>
  22 Cc: Peter Zijlstra <peterz@infradead.org>
  23 Cc: Andy Lutomirski <luto@kernel.org>
  24 Cc: Linus Torvalds <torvalds@linux-foundation.org>
  25 Cc: Jiri Kosina <jkosina@suse.cz>
  26 Cc: Tom Lendacky <thomas.lendacky@amd.com>
  27 Cc: Josh Poimboeuf <jpoimboe@redhat.com>
  28 Cc: Andrea Arcangeli <aarcange@redhat.com>
  29 Cc: David Woodhouse <dwmw@amazon.co.uk>
  30 Cc: Tim Chen <tim.c.chen@linux.intel.com>
  31 Cc: Andi Kleen <ak@linux.intel.com>
  32 Cc: Dave Hansen <dave.hansen@intel.com>
  33 Cc: Casey Schaufler <casey.schaufler@intel.com>
  34 Cc: Asit Mallick <asit.k.mallick@intel.com>
  35 Cc: Arjan van de Ven <arjan@linux.intel.com>
  36 Cc: Jon Masters <jcm@redhat.com>
  37 Cc: Waiman Long <longman9394@gmail.com>
  38 Cc: Greg KH <gregkh@linuxfoundation.org>
  39 Cc: Dave Stewart <david.c.stewart@intel.com>
  40 Cc: Kees Cook <keescook@chromium.org>
  41 Link: https://lkml.kernel.org/r/20181125185004.521974984@linutronix.de
  42 [bwh: Backported to 4.4: adjust context]
  43 Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
  44 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  45 ---
  46  arch/x86/kernel/cpu/bugs.c |   11 +++++------
  47  include/linux/sched/smt.h  |    2 ++
  48  kernel/cpu.c               |   10 +++++++++-
  49  3 files changed, 16 insertions(+), 7 deletions(-)
  50
  51 --- a/arch/x86/kernel/cpu/bugs.c
  52 +++ b/arch/x86/kernel/cpu/bugs.c
  53 @@ -13,6 +13,7 @@
  54  #include <linux/module.h>
  55  #include <linux/nospec.h>
  56  #include <linux/prctl.h>
  57 +#include <linux/sched/smt.h>
  58
  59  #include <asm/spec-ctrl.h>
  60  #include <asm/cmdline.h>
  61 @@ -340,16 +341,14 @@ void arch_smt_update(void)
  62                 return;
  63
  64         mutex_lock(&spec_ctrl_mutex);
  65 -       mask = x86_spec_ctrl_base;
  66 -       if (IS_ENABLED(CONFIG_SMP))
  67 +
  68 +       mask = x86_spec_ctrl_base & ~SPEC_CTRL_STIBP;
  69 +       if (sched_smt_active())
  70                 mask |= SPEC_CTRL_STIBP;
  71 -       else
  72 -               mask &= ~SPEC_CTRL_STIBP;
  73
  74         if (mask != x86_spec_ctrl_base) {
  75                 pr_info("Spectre v2 cross-process SMT mitigation: %s STIBP\n",
  76 -                               IS_ENABLED(CONFIG_SMP) ?
  77 -                               "Enabling" : "Disabling");
  78 +                       mask & SPEC_CTRL_STIBP ? "Enabling" : "Disabling");
  79                 x86_spec_ctrl_base = mask;
  80                 on_each_cpu(update_stibp_msr, NULL, 1);
  81         }
  82 --- a/include/linux/sched/smt.h
  83 +++ b/include/linux/sched/smt.h
  84 @@ -15,4 +15,6 @@ static __always_inline bool sched_smt_ac
  85  static inline bool sched_smt_active(void) { return false; }
  86  #endif
  87
  88 +void arch_smt_update(void);
  89 +
  90  #endif
  91 --- a/kernel/cpu.c
  92 +++ b/kernel/cpu.c
  93 @@ -8,6 +8,7 @@
  94  #include <linux/init.h>
  95  #include <linux/notifier.h>
  96  #include <linux/sched.h>
  97 +#include <linux/sched/smt.h>
  98  #include <linux/unistd.h>
  99  #include <linux/cpu.h>
 100  #include <linux/oom.h>
 101 @@ -199,6 +200,12 @@ void cpu_hotplug_enable(void)
 102  EXPORT_SYMBOL_GPL(cpu_hotplug_enable);
 103  #endif /* CONFIG_HOTPLUG_CPU */
 104
 105 +/*
 106 + * Architectures that need SMT-specific errata handling during SMT hotplug
 107 + * should override this.
 108 + */
 109 +void __weak arch_smt_update(void) { }
 110 +
 111  /* Need to know about CPUs going up/down? */
 112  int register_cpu_notifier(struct notifier_block *nb)
 113  {
 114 @@ -434,6 +441,7 @@ out_release:
 115         cpu_hotplug_done();
 116         if (!err)
 117                 cpu_notify_nofail(CPU_POST_DEAD | mod, hcpu);
 118 +       arch_smt_update();
 119         return err;
 120  }
 121
 122 @@ -537,7 +545,7 @@ out_notify:
 123                 __cpu_notify(CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
 124  out:
 125         cpu_hotplug_done();
 126 -
 127 +       arch_smt_update();
 128         return ret;
 129  }
 130