Author: jkim
Date: Thu Apr 14 17:50:26 2011
New Revision: 220637
URL: http://svn.freebsd.org/changeset/base/220637
Log:
Work around an emulator problem where virtual CPU advertises TSC is P-state
invariant and APERF/MPERF MSRs exist but these MSRs never tick. When we
calculate effective frequency from cpu_est_clockrate(), it caused panic of
division-by-zero. Now we test whether these MSRs actually increase to avoid
such foot-shooting.
Reported by: dim
Tested by: dim
Modified:
head/sys/x86/x86/tsc.c
Modified: head/sys/x86/x86/tsc.c
==============================================================================
--- head/sys/x86/x86/tsc.c Thu Apr 14 17:42:21 2011 (r220636)
+++ head/sys/x86/x86/tsc.c Thu Apr 14 17:50:26 2011 (r220637)
@@ -183,8 +183,18 @@ probe_tsc_freq(void)
if (cpu_high >= 6) {
do_cpuid(6, regs);
- if ((regs[2] & CPUID_PERF_STAT) != 0)
- tsc_perf_stat = 1;
+ if ((regs[2] & CPUID_PERF_STAT) != 0) {
+ /*
+ * XXX Some emulators expose host CPUID without actual
+ * support for these MSRs. We must test whether they
+ * really work.
+ */
+ wrmsr(MSR_MPERF, 0);
+ wrmsr(MSR_APERF, 0);
+ DELAY(10);
+ if (rdmsr(MSR_MPERF) > 0 && rdmsr(MSR_APERF) > 0)
+ tsc_perf_stat = 1;
+ }
}
if (tsc_skip_calibration) {
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