hv: export current Hyper-V clocksource

As a preparation to implementing Hyper-V PTP device supporting
.getcrosststamp we need to export a reference to the current Hyper-V
clocksource in use (MSR or TSC page).

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 9 insertions, 4 deletions

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index b371d0e984a9..c224b7df4d21 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -99,6 +99,9 @@ static struct clocksource hyperv_cs_msr = {
 };
 
 static void *hypercall_pg;
+struct clocksource *hyperv_cs;
+EXPORT_SYMBOL_GPL(hyperv_cs);
+
 /*
  * This function is to be invoked early in the boot sequence after the
  * hypervisor has been detected.
@@ -141,10 +144,10 @@ void hyperv_init(void)
 		union hv_x64_msr_hypercall_contents tsc_msr;
 
 		tsc_pg = __vmalloc(PAGE_SIZE, GFP_KERNEL, PAGE_KERNEL);
-		if (!tsc_pg) {
-			clocksource_register_hz(&hyperv_cs_msr, NSEC_PER_SEC/100);
-			return;
-		}
+		if (!tsc_pg)
+			goto register_msr_cs;
+
+		hyperv_cs = &hyperv_cs_tsc;
 
 		rdmsrl(HV_X64_MSR_REFERENCE_TSC, tsc_msr.as_uint64);
 
@@ -161,6 +164,8 @@ void hyperv_init(void)
 	 * the partition counter.
 	 */
 
+register_msr_cs:
+	hyperv_cs = &hyperv_cs_msr;
 	if (ms_hyperv.features & HV_X64_MSR_TIME_REF_COUNT_AVAILABLE)
 		clocksource_register_hz(&hyperv_cs_msr, NSEC_PER_SEC/100);
 }