Use CPUID leaf 0x40000010 for local APIC freq

Some VM systems announce the frequency of the local APIC via the
CPUID leaf 0x40000010.  Using this allows us to boot slightly
faster by avoiding the need for timer calibration.

Reviewed by:	markj
Sponsored by:	https://www.patreon.com/cperciva

(cherry picked from commit de1292c6ff8a445fd453effba8cc23c38cea223f)

1 files changed, 33 insertions, 0 deletions

diff --git a/sys/x86/x86/local_apic.c b/sys/x86/x86/local_apic.c
index c5f72a7ff43c..59b5cb600725 100644
--- a/sys/x86/x86/local_apic.c
+++ b/sys/x86/x86/local_apic.c
@@ -991,6 +991,35 @@ native_lapic_disable_pmc(void)
 #endif
 }
 
+static int
+lapic_calibrate_initcount_cpuid_vm(void)
+{
+	u_int regs[4];
+	uint64_t freq;
+
+	/* Get value from CPUID leaf if possible. */
+	if (vm_guest == VM_GUEST_NO)
+		return (false);
+	if (hv_high < 0x40000010)
+		return (false);
+	do_cpuid(0x40000010, regs);
+	freq = (uint64_t)(regs[1]) * 1000;
+
+	/* Pick timer divisor. */
+	lapic_timer_divisor = 2;
+	do {
+		if (freq / lapic_timer_divisor < APIC_TIMER_MAX_COUNT)
+			break;
+		lapic_timer_divisor <<= 1;
+	} while (lapic_timer_divisor <= 128);
+	if (lapic_timer_divisor > 128)
+		return (false);
+
+	/* Record divided frequency. */
+	count_freq = freq / lapic_timer_divisor;
+	return (true);
+}
+
 static uint64_t
 cb_lapic_getcount(void)
 {
@@ -1003,6 +1032,9 @@ lapic_calibrate_initcount(struct lapic *la)
 {
 	uint64_t freq;
 
+	if (lapic_calibrate_initcount_cpuid_vm())
+		goto done;
+
 	/* Calibrate the APIC timer frequency. */
 	lapic_timer_set_divisor(2);
 	lapic_timer_oneshot_nointr(la, APIC_TIMER_MAX_COUNT);
@@ -1020,6 +1052,7 @@ lapic_calibrate_initcount(struct lapic *la)
 	if (lapic_timer_divisor > 128)
 		panic("lapic: Divisor too big");
 	count_freq = freq * 2 / lapic_timer_divisor;
+done:
 	if (bootverbose) {
 		printf("lapic: Divisor %lu, Frequency %lu Hz\n",
 		    lapic_timer_divisor, count_freq);