Merge branch 'perf-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'perf-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  perf: Fix the software context switch counter
  perf, x86: Fixup Kconfig deps
  x86, perf, nmi: Disable perf if counters are not accessible
  perf: Fix inherit vs. context rotation bug

2 files changed, 21 insertions, 1 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index e8327686d3c5..e330da21b84f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -21,7 +21,7 @@ config X86
         select HAVE_UNSTABLE_SCHED_CLOCK
         select HAVE_IDE
         select HAVE_OPROFILE
-        select HAVE_PERF_EVENTS if (!M386 && !M486)
+        select HAVE_PERF_EVENTS
         select HAVE_IRQ_WORK
         select HAVE_IOREMAP_PROT
         select HAVE_KPROBES
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index ed6310183efb..6d75b9145b13 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -381,6 +381,20 @@ static void release_pmc_hardware(void) {}
 
 #endif
 
+static bool check_hw_exists(void)
+{
+        u64 val, val_new = 0;
+        int ret = 0;
+
+        val = 0xabcdUL;
+        ret |= checking_wrmsrl(x86_pmu.perfctr, val);
+        ret |= rdmsrl_safe(x86_pmu.perfctr, &val_new);
+        if (ret || val != val_new)
+                return false;
+
+        return true;
+}
+
 static void reserve_ds_buffers(void);
 static void release_ds_buffers(void);
 
@@ -1372,6 +1386,12 @@ void __init init_hw_perf_events(void)
 
         pmu_check_apic();
 
+        /* sanity check that the hardware exists or is emulated */
+        if (!check_hw_exists()) {
+                pr_cont("Broken PMU hardware detected, software events only.\n");
+                return;
+        }
+
         pr_cont("%s PMU driver.\n", x86_pmu.name);
 
         if (x86_pmu.quirks)