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Date:      Wed, 15 Apr 2020 00:36:00 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-12@freebsd.org
Subject:   svn commit: r359947 - stable/12/sys/x86/x86
Message-ID:  <202004150036.03F0a0n8052280@repo.freebsd.org>
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Author: kib
Date: Wed Apr 15 00:36:00 2020
New Revision: 359947
URL: https://svnweb.freebsd.org/changeset/base/359947

Log:
  MFC r359520:
  x86 tsc: fall back to CPUID if calibration results looks unbelievable.

Modified:
  stable/12/sys/x86/x86/tsc.c
Directory Properties:
  stable/12/   (props changed)

Modified: stable/12/sys/x86/x86/tsc.c
==============================================================================
--- stable/12/sys/x86/x86/tsc.c	Wed Apr 15 00:18:19 2020	(r359946)
+++ stable/12/sys/x86/x86/tsc.c	Wed Apr 15 00:36:00 2020	(r359947)
@@ -142,7 +142,7 @@ tsc_freq_vmware(void)
  * tsc_freq_intel(), when available.
  */
 static bool
-tsc_freq_cpuid(void)
+tsc_freq_cpuid(uint64_t *res)
 {
 	u_int regs[4];
 
@@ -150,7 +150,7 @@ tsc_freq_cpuid(void)
 		return (false);
 	do_cpuid(0x15, regs);
 	if (regs[0] != 0 && regs[1] != 0 && regs[2] != 0) {
-		tsc_freq = (uint64_t)regs[2] * regs[1] / regs[0];
+		*res = (uint64_t)regs[2] * regs[1] / regs[0];
 		return (true);
 	}
 
@@ -158,7 +158,7 @@ tsc_freq_cpuid(void)
 		return (false);
 	do_cpuid(0x16, regs);
 	if (regs[0] != 0) {
-		tsc_freq = (uint64_t)regs[0] * 1000000;
+		*res = (uint64_t)regs[0] * 1000000;
 		return (true);
 	}
 
@@ -228,7 +228,8 @@ static void
 probe_tsc_freq(void)
 {
 	u_int regs[4];
-	uint64_t tsc1, tsc2;
+	uint64_t tmp_freq, tsc1, tsc2;
+	int no_cpuid_override;
 	uint16_t bootflags;
 
 	if (cpu_high >= 6) {
@@ -303,15 +304,15 @@ probe_tsc_freq(void)
 		 */
 		if (acpi_get_fadt_bootflags(&bootflags) &&
 		    (bootflags & ACPI_FADT_LEGACY_DEVICES) == 0 &&
-		    tsc_freq_cpuid()) {
+		    tsc_freq_cpuid(&tmp_freq)) {
 			printf("Skipping TSC calibration since no legacy "
 			    "devices reported by FADT and CPUID works\n");
 			tsc_skip_calibration = 1;
 		}
 	}
 	if (tsc_skip_calibration) {
-		if (tsc_freq_cpuid())
-			;
+		if (tsc_freq_cpuid(&tmp_freq))
+			tsc_freq = tmp_freq;
 		else if (cpu_vendor_id == CPU_VENDOR_INTEL)
 			tsc_freq_intel();
 	} else {
@@ -321,6 +322,32 @@ probe_tsc_freq(void)
 		DELAY(1000000);
 		tsc2 = rdtsc();
 		tsc_freq = tsc2 - tsc1;
+
+		/*
+		 * If the difference between calibrated frequency and
+		 * the frequency reported by CPUID 0x15/0x16 leafs
+		 * differ significantly, this probably means that
+		 * calibration is bogus.  It happens on machines
+		 * without 8254 timer and with BIOS not properly
+		 * reporting it in FADT boot flags.
+		 */
+		if (tsc_freq_cpuid(&tmp_freq) && qabs(tsc_freq - tmp_freq) >
+		    uqmin(tsc_freq, tmp_freq)) {
+			no_cpuid_override = 0;
+			TUNABLE_INT_FETCH("machdep.disable_tsc_cpuid_override",
+			    &no_cpuid_override);
+			if (!no_cpuid_override) {
+				if (bootverbose) {
+					printf(
+	"TSC clock: calibration freq %ju Hz, CPUID freq %ju Hz%s\n",
+					    (uintmax_t)tsc_freq,
+					    (uintmax_t)tmp_freq,
+					    no_cpuid_override ? "" :
+					    ", doing CPUID override");
+				}
+				tsc_freq = tmp_freq;
+			}
+		}
 	}
 	if (bootverbose)
 		printf("TSC clock: %ju Hz\n", (intmax_t)tsc_freq);

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