git: a605a66017ec - stable/13 - Use CPUID leaf 0x40000010 for local APIC freq

The branch stable/13 has been updated by cperciva:

URL: https://cgit.FreeBSD.org/src/commit/?id=a605a66017ec53e42c06b35a1786edf1b33cd8ab

commit a605a66017ec53e42c06b35a1786edf1b33cd8ab
Author:     Colin Percival <cperciva@FreeBSD.org>
AuthorDate: 2022-01-09 00:59:31 +0000
Commit:     Colin Percival <cperciva@FreeBSD.org>
CommitDate: 2022-02-11 06:52:00 +0000

    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)
---
 sys/x86/x86/local_apic.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

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);