x86/hyperv: Initialize clockevents earlier in CPU onlining

Hyper-V has historically initialized stimer-based clockevents late in the
process of onlining a CPU because clockevents depend on stimer
interrupts. In the original Hyper-V design, stimer interrupts generate a
VMbus message, so the VMbus machinery must be running first, and VMbus
can't be initialized until relatively late. On x86/64, LAPIC timer based
clockevents are used during early initialization before VMbus and
stimer-based clockevents are ready, and again during CPU offlining after
the stimer clockevents have been shut down.

Unfortunately, this design creates problems when offlining CPUs for
hibernation or other purposes. stimer-based clockevents are shut down
relatively early in the offlining process, so clockevents_unbind_device()
must be used to fallback to the LAPIC-based clockevents for the remainder
of the offlining process.  Furthermore, the late initialization and early
shutdown of stimer-based clockevents doesn't work well on ARM64 since there
is no other timer like the LAPIC to fallback to. So CPU onlining and
offlining doesn't work properly.

Fix this by recognizing that stimer Direct Mode is the normal path for
newer versions of Hyper-V on x86/64, and the only path on other
architectures. With stimer Direct Mode, stimer interrupts don't require any
VMbus machinery. stimer clockevents can be initialized and shut down
consistent with how it is done for other clockevent devices. While the old
VMbus-based stimer interrupts must still be supported for backward
compatibility on x86, that mode of operation can be treated as legacy.

So add a new Hyper-V stimer entry in the CPU hotplug state list, and use
that new state when in Direct Mode. Update the Hyper-V clocksource driver
to allocate and initialize stimer clockevents earlier during boot. Update
Hyper-V initialization and the VMbus driver to use this new design. As a
result, the LAPIC timer is no longer used during boot or CPU
onlining/offlining and clockevents_unbind_device() is not called.  But
retain the old design as a legacy implementation for older versions of
Hyper-V that don't support Direct Mode.

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Dexuan Cui <decui@microsoft.com>
Link: https://lkml.kernel.org/r/1573607467-9456-1-git-send-email-mikelley@microsoft.com

1 files changed, 14 insertions, 16 deletions

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 53a60c81e220..8c06b3361c27 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1340,10 +1340,6 @@ static int vmbus_bus_init(void)
 	if (ret)
 		goto err_alloc;
 
-	ret = hv_stimer_alloc(VMBUS_MESSAGE_SINT);
-	if (ret < 0)
-		goto err_alloc;
-
 	/*
 	 * Initialize the per-cpu interrupt state and stimer state.
 	 * Then connect to the host.
@@ -1400,9 +1396,8 @@ static int vmbus_bus_init(void)
 err_connect:
 	cpuhp_remove_state(hyperv_cpuhp_online);
 err_cpuhp:
-	hv_stimer_free();
-err_alloc:
 	hv_synic_free();
+err_alloc:
 	hv_remove_vmbus_irq();
 
 	bus_unregister(&hv_bus);
@@ -2315,20 +2310,23 @@ static void hv_crash_handler(struct pt_regs *regs)
 static int hv_synic_suspend(void)
 {
 	/*
-	 * When we reach here, all the non-boot CPUs have been offlined, and
-	 * the stimers on them have been unbound in hv_synic_cleanup() ->
+	 * When we reach here, all the non-boot CPUs have been offlined.
+	 * If we're in a legacy configuration where stimer Direct Mode is
+	 * not enabled, the stimers on the non-boot CPUs have been unbound
+	 * in hv_synic_cleanup() -> hv_stimer_legacy_cleanup() ->
 	 * hv_stimer_cleanup() -> clockevents_unbind_device().
 	 *
-	 * hv_synic_suspend() only runs on CPU0 with interrupts disabled. Here
-	 * we do not unbind the stimer on CPU0 because: 1) it's unnecessary
-	 * because the interrupts remain disabled between syscore_suspend()
-	 * and syscore_resume(): see create_image() and resume_target_kernel();
+	 * hv_synic_suspend() only runs on CPU0 with interrupts disabled.
+	 * Here we do not call hv_stimer_legacy_cleanup() on CPU0 because:
+	 * 1) it's unnecessary as interrupts remain disabled between
+	 * syscore_suspend() and syscore_resume(): see create_image() and
+	 * resume_target_kernel()
 	 * 2) the stimer on CPU0 is automatically disabled later by
 	 * syscore_suspend() -> timekeeping_suspend() -> tick_suspend() -> ...
-	 * -> clockevents_shutdown() -> ... -> hv_ce_shutdown(); 3) a warning
-	 * would be triggered if we call clockevents_unbind_device(), which
-	 * may sleep, in an interrupts-disabled context. So, we intentionally
-	 * don't call hv_stimer_cleanup(0) here.
+	 * -> clockevents_shutdown() -> ... -> hv_ce_shutdown()
+	 * 3) a warning would be triggered if we call
+	 * clockevents_unbind_device(), which may sleep, in an
+	 * interrupts-disabled context.
 	 */
 
 	hv_synic_disable_regs(0);