[patch 1/3] KVM: x86: provide realtime host clock via vsyscall notifiers

[Marcelo Tosatti]

Expose the realtime host clock and save the TSC value
used for the clock calculation.

Signed-off-by: Marcelo Tosatti <mtosa...@redhat.com>

---
 arch/x86/kvm/x86.c |   38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

Index: kvm-ptpdriver/arch/x86/kvm/x86.c
===================================================================
--- kvm-ptpdriver.orig/arch/x86/kvm/x86.c       2017-01-13 08:59:03.015895353 
-0200
+++ kvm-ptpdriver/arch/x86/kvm/x86.c    2017-01-13 09:04:46.581415259 -0200
@@ -1139,6 +1139,8 @@
 
        u64             boot_ns;
        u64             nsec_base;
+       u64             wall_time_sec;
+       u64             wall_time_snsec;
 };
 
 static struct pvclock_gtod_data pvclock_gtod_data;
@@ -1162,6 +1164,9 @@
        vdata->boot_ns                  = boot_ns;
        vdata->nsec_base                = tk->tkr_mono.xtime_nsec;
 
+       vdata->wall_time_sec            = tk->xtime_sec;
+       vdata->wall_time_snsec          = tk->tkr_mono.xtime_nsec;
+
        write_seqcount_end(&vdata->seq);
 }
 #endif
@@ -1623,6 +1628,28 @@
        return mode;
 }
 
+static int do_realtime(struct timespec *ts, cycle_t *cycle_now)
+{
+       struct pvclock_gtod_data *gtod = &pvclock_gtod_data;
+       unsigned long seq;
+       int mode;
+       u64 ns;
+
+       do {
+               seq = read_seqcount_begin(&gtod->seq);
+               mode = gtod->clock.vclock_mode;
+               ts->tv_sec = gtod->wall_time_sec;
+               ns = gtod->wall_time_snsec;
+               ns += vgettsc(cycle_now);
+               ns >>= gtod->clock.shift;
+       } while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
+
+       ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
+       ts->tv_nsec = ns;
+
+       return mode;
+}
+
 /* returns true if host is using tsc clocksource */
 static bool kvm_get_time_and_clockread(s64 *kernel_ns, cycle_t *cycle_now)
 {
@@ -1632,6 +1659,17 @@
 
        return do_monotonic_boot(kernel_ns, cycle_now) == VCLOCK_TSC;
 }
+
+/* returns true if host is using tsc clocksource */
+static bool kvm_get_walltime_and_clockread(struct timespec *ts,
+                                          cycle_t *cycle_now)
+{
+       /* checked again under seqlock below */
+       if (pvclock_gtod_data.clock.vclock_mode != VCLOCK_TSC)
+               return false;
+
+       return do_realtime(ts, cycle_now) == VCLOCK_TSC;
+}
 #endif
 
 /*