[RFC 6/8] kvm steal time implementation

[Glauber Costa <glommer@redhat.com>]

This is the proposed kvm-side steal time implementation.
It is migration safe, as it checks flags at every read.

Signed-off-by: Glauber Costa <glommer@redhat.com>
---
 arch/x86/kernel/kvmclock.c |   35 +++++++++++++++++++++++++++++++++++
 1 files changed, 35 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index eb9b76c..a1f4852 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -18,6 +18,8 @@
 
 #include <linux/clocksource.h>
 #include <linux/kvm_para.h>
+#include <linux/kernel_stat.h>
+#include <linux/sched.h>
 #include <asm/pvclock.h>
 #include <asm/msr.h>
 #include <asm/apic.h>
@@ -41,6 +43,7 @@ early_param("no-kvmclock", parse_no_kvmclock);
 
 /* The hypervisor will put information about time periodically here */
 static DEFINE_PER_CPU_SHARED_ALIGNED(struct pvclock_vcpu_time_info, hv_clock);
+static DEFINE_PER_CPU(u64, steal_info);
 static struct pvclock_wall_clock wall_clock;
 
 /*
@@ -82,6 +85,32 @@ static cycle_t kvm_clock_read(void)
 	return ret;
 }
 
+static DEFINE_PER_CPU(u64, steal_info);
+
+cputime_t kvm_get_steal_time(void)
+{
+	u64 delta = 0;
+	u64 *last_steal_info, this_steal_info;
+	struct pvclock_vcpu_time_info *src;
+
+	src = &get_cpu_var(hv_clock);
+	if (!(src->flags & PVCLOCK_STEAL_BIT))
+		goto out;
+
+	this_steal_info = src->steal_time;
+	put_cpu_var(hv_clock);
+
+	last_steal_info = &get_cpu_var(steal_info);
+
+	delta = this_steal_info - *last_steal_info;
+
+	*last_steal_info = this_steal_info;
+	put_cpu_var(steal_info);
+
+out:
+	return msecs_to_cputime(delta);
+}
+
 static cycle_t kvm_clock_get_cycles(struct clocksource *cs)
 {
 	return kvm_clock_read();
@@ -134,6 +163,8 @@ static int kvm_register_clock(char *txt)
 	printk(KERN_INFO "kvm-clock: cpu %d, msr %x:%x, %s\n",
 	       cpu, high, low, txt);
 
+	per_cpu(steal_info, cpu) = 0;
+
 	return native_write_msr_safe(msr_kvm_system_time, low, high);
 }
 
@@ -218,4 +249,8 @@ void __init kvmclock_init(void)
 
 	if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STABLE_BIT))
 		pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);
+
+	
+	if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STEAL_BIT))
+		hypervisor_steal_time = kvm_get_steal_time;
 }
-- 
1.6.2.2