inmates: x86: Add support for TSC-based timing

Provide a service to calibrate the TSC against the PM timer and read out
the current time in nanoseconds. This service is much faster than the
slow PM timer, and it's also not affected by chipset-induced delays.

Note that the simplistic algorithm only supports measuring relative time
spans of a couple of seconds.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

inmates/lib/x86/inmate.h

@@ -230,7 +230,12 @@ void inmate_main(void);
 void hypercall_init(void);
 
 unsigned long pm_timer_read(void);
+
+unsigned long tsc_read(void);
+unsigned long tsc_init(void);
+
 void delay_us(unsigned long microsecs);
+
 unsigned long apic_timer_init(unsigned int vector);
 void apic_timer_set(unsigned long timeout_ns);
 

inmates/lib/x86/timing.c

@@ -23,6 +23,58 @@
 static unsigned long divided_apic_freq;
 static unsigned long pm_timer_last[SMP_MAX_CPUS];
 static unsigned long pm_timer_overflows[SMP_MAX_CPUS];
+static unsigned long tsc_freq, tsc_overflow;
+static unsigned long tsc_last[SMP_MAX_CPUS];
+static unsigned long tsc_overflows[SMP_MAX_CPUS];
+
+static u64 rdtsc(void)
+{
+#ifdef __x86_64__
+	u32 lo, hi;
+
+	asm volatile("rdtsc" : "=a" (lo), "=d" (hi));
+	return (u64)lo | (((u64)hi) << 32);
+#else
+	u64 v;
+
+	asm volatile("rdtsc" : "=A" (v));
+	return v;
+#endif
+}
+
+unsigned long tsc_read(void)
+{
+	unsigned int cpu = cpu_id();
+	unsigned long tmr;
+
+	tmr = ((rdtsc() & 0xffffffffLL) * NS_PER_SEC) / tsc_freq;
+	if (tmr < tsc_last[cpu])
+		tsc_overflows[cpu] += tsc_overflow;
+	tsc_last[cpu] = tmr;
+	return tmr + tsc_overflows[cpu];
+}
+
+unsigned long tsc_init(void)
+{
+	unsigned long start_pm, end_pm;
+	u64 start_tsc, end_tsc;
+
+	start_pm = pm_timer_read();
+	start_tsc = rdtsc();
+	asm volatile("mfence" : : : "memory");
+
+	while (pm_timer_read() - start_pm < 100 * NS_PER_MSEC)
+		cpu_relax();
+
+	end_pm = pm_timer_read();
+	end_tsc = rdtsc();
+	asm volatile("mfence" : : : "memory");
+
+	tsc_freq = (end_tsc - start_tsc) * NS_PER_SEC / (end_pm - start_pm);
+	tsc_overflow = (0x100000000L * NS_PER_SEC) / tsc_freq;
+
+	return tsc_freq;
+}
 
 unsigned long pm_timer_read(void)
 {