Reading QEMU_CLOCK_VIRTUAL is thread-safe, write access is NOP.

This makes possible to boot Windows with large vCPUs count when
hv-time is not used.

Reproducer:
  -M q35,hpet=off -cpu host -enable-kvm -smp 240,sockets=4 -m 8G WS2025.img
fails to boot within 30min.

With this fix it boots within 2-1min.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
 hw/acpi/core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/hw/acpi/core.c b/hw/acpi/core.c
index 58f8964e13..ff16582803 100644
--- a/hw/acpi/core.c
+++ b/hw/acpi/core.c
@@ -547,6 +547,7 @@ void acpi_pm_tmr_init(ACPIREGS *ar, acpi_update_sci_fn update_sci,
     ar->tmr.timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, acpi_pm_tmr_timer, ar);
     memory_region_init_io(&ar->tmr.io, memory_region_owner(parent),
                           &acpi_pm_tmr_ops, ar, "acpi-tmr", 4);
+    memory_region_enable_lockless_io(&ar->tmr.io);
     memory_region_add_subregion(parent, 8, &ar->tmr.io);
 }
 
-- 
2.47.1