[PATCH 6/7] xen: Enable PV clocksource for HVM

[Sheng Yang]

PV clocksource can provide a reliable clocksource for HVM running on Xen.

To enable it, put following line to the HVM configure file:

cpuid = [ '0x40000002:edx=0x3' ]

It would set bit 0 and bit 1 in 0x40000002:edx, which enable PV extension
framework and PV clocksource.

Signed-off-by: Sheng Yang <sheng@xxxxxxxxxxxxxxx>
---
 arch/x86/xen/hvmpv.c   |   24 ++++++++++++++++++++++++
 arch/x86/xen/time.c    |   12 +++++++++++-
 arch/x86/xen/xen-ops.h |    1 +
 3 files changed, 36 insertions(+), 1 deletions(-)

diff --git a/arch/x86/xen/hvmpv.c b/arch/x86/xen/hvmpv.c
index 540eef4..e944caf 100644
--- a/arch/x86/xen/hvmpv.c
+++ b/arch/x86/xen/hvmpv.c
@@ -43,6 +43,8 @@ static void __init xen_hvm_pv_banner(void)
 		pv_info.name);
 	printk(KERN_INFO "Xen version: %d.%d%s\n",
 		version >> 16, version & 0xffff, extra.extraversion);
+	if (xen_hvm_pv_clock_enabled())
+		printk(KERN_INFO "PV feature: PV clocksource enabled\n");
 }
 
 static int __init xen_para_available(void)
@@ -82,6 +84,9 @@ static int __init init_hvm_pv_info(void)
 	if (!(edx & XEN_CPUID_FEAT2_HVM_PV))
 		return -ENODEV;
 
+	if (edx & XEN_CPUID_FEAT2_HVM_PV_CLOCK)
+		xen_hvm_pv_features |= XEN_HVM_PV_CLOCK_ENABLED;
+
 	if (pages < 1)
 		return -ENODEV;
 
@@ -112,6 +117,23 @@ static int __init init_shared_info(void)
 	return 0;
 }
 
+static void __init init_pv_clocksource(void)
+{
+	if (!xen_hvm_pv_clock_enabled())
+		return;
+
+	if (enable_hvm_pv(HVM_PV_CLOCK))
+		BUG();
+
+	pv_time_ops.sched_clock = xen_sched_clock;
+
+	x86_platform.calibrate_tsc = xen_tsc_khz;
+	x86_platform.get_wallclock = xen_get_wallclock;
+	x86_platform.set_wallclock = xen_set_wallclock;
+
+	xen_register_clocksource();
+}
+
 void __init xen_guest_init(void)
 {
 	int r;
@@ -134,4 +156,6 @@ void __init xen_guest_init(void)
 	pv_info = xen_hvm_pv_info;
 
 	xen_domain_type = XEN_HVM_DOMAIN;
+
+	init_pv_clocksource();
 }
diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index 0d3f07c..06b3e72 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -472,11 +472,21 @@ void xen_timer_resume(void)
 	}
 }
 
+static bool xen_clocksource_enabled;
+
+void xen_register_clocksource(void)
+{
+	if (!xen_clocksource_enabled) {
+		clocksource_register(&xen_clocksource);
+		xen_clocksource_enabled = 1;
+	}
+}
+
 __init void xen_time_init(void)
 {
 	int cpu = smp_processor_id();
 
-	clocksource_register(&xen_clocksource);
+	xen_register_clocksource();
 
 	if (HYPERVISOR_vcpu_op(VCPUOP_stop_periodic_timer, cpu, NULL) == 0) {
 		/* Successfully turned off 100Hz tick, so we have the
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index f9153a3..d56b660 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -48,6 +48,7 @@ cycle_t xen_clocksource_read(void);
 void xen_setup_cpu_clockevents(void);
 unsigned long xen_tsc_khz(void);
 void __init xen_time_init(void);
+void xen_register_clocksource(void);
 unsigned long xen_get_wallclock(void);
 int xen_set_wallclock(unsigned long time);
 unsigned long long xen_sched_clock(void);
-- 
1.5.4.5

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