linux-kernel - [PATCH v4 10/10] kvmclock: implement the extended reading function

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Date:   Wed,  2 Aug 2017 17:38:10 +0300
From:   Denis Plotnikov <dplotnikov@...tuozzo.com>
To:     pbonzini@...hat.com, rkrcmar@...hat.com, kvm@...r.kernel.org,
        john.stultz@...aro.org, tglx@...utronix.de
Cc:     mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
        x86@...nel.org, rkagan@...tuozzo.com, den@...tuozzo.com
Subject: [PATCH v4 10/10] kvmclock: implement the extended reading function

This allows L2 guests to use masterclock, namely
provide KVM with ability to use masterclock while
running over kvmclock closksource in the cases when
it's possible.

This is the final part of the work of teaching KVM
to use masterclock when over kvmclock clocksource.

Signed-off-by: Denis Plotnikov <dplotnikov@...tuozzo.com>
---
 arch/x86/kernel/kvmclock.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index f692579..8c1008f 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -82,7 +82,7 @@ static int kvm_set_wallclock(const struct timespec *now)
 	return -1;
 }
 
-static u64 kvm_clock_read(void)
+static inline u64 __kvm_clock_read(u64 *cycles, u8 *flags)
 {
 	struct pvclock_vcpu_time_info *src;
 	u64 ret;
@@ -91,10 +91,14 @@ static u64 kvm_clock_read(void)
 	preempt_disable_notrace();
 	cpu = smp_processor_id();
 	src = &hv_clock[cpu].pvti;
-	ret = pvclock_clocksource_read(src, NULL, NULL);
+	ret = pvclock_clocksource_read(src, cycles, flags);
 	preempt_enable_notrace();
 	return ret;
 }
+static u64 kvm_clock_read(void)
+{
+	return __kvm_clock_read(NULL, NULL);
+}
 
 static u64 kvm_clock_get_cycles(struct clocksource *cs)
 {
@@ -177,9 +181,20 @@ bool kvm_check_and_clear_guest_paused(void)
 	return ret;
 }
 
+static bool kvm_clock_read_with_stamp(struct clocksource *cs,
+					u64 *cycles, u64 *cycles_stamp)
+{
+	u8 flags;
+
+	*cycles = __kvm_clock_read(cycles_stamp, &flags);
+
+	return (bool) flags & PVCLOCK_TSC_STABLE_BIT;
+}
+
 struct clocksource kvm_clock = {
 	.name = "kvm-clock",
 	.read = kvm_clock_get_cycles,
+	.read_with_stamp = kvm_clock_read_with_stamp,
 	.rating = 400,
 	.mask = CLOCKSOURCE_MASK(64),
 	.flags = CLOCK_SOURCE_IS_CONTINUOUS,
-- 
2.7.4