[RESEND] ACPI / processor_idle: use dead loop instead of io port access for wait

[Yin Fengwei]

In function acpi_idle_do_entry(), we do an io port access to guarantee
hardware behavior. But it could trigger unnecessary vmexit for
virtualization environemnt.

>From the comments of this part of code, we could use busy wait instead
of io port access to guarantee hardware behavior and avoid unnecessary
vmexit.

Signed-off-by: Yin Fengwei <fengwei....@intel.com>
---
 drivers/acpi/processor_idle.c | 33 ++++++++++++++++++++++++++++++---
 1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index ed56c6d20b08..676553228e8f 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -55,6 +55,8 @@ struct cpuidle_driver acpi_idle_driver = {
 };
 
 #ifdef CONFIG_ACPI_PROCESSOR_CSTATE
+static struct timespec64 dummy_delta = {0L, 0L};
+
 static
 DEFINE_PER_CPU(struct acpi_processor_cx * [CPUIDLE_STATE_MAX], acpi_cstate);
 
@@ -64,6 +66,18 @@ static int disabled_by_idle_boot_param(void)
                boot_option_idle_override == IDLE_HALT;
 }
 
+static void dummy_wait(void)
+{
+       struct timespec64 now, target;
+
+       ktime_get_real_ts64(&now);
+       target = timespec64_add(now, dummy_delta);
+
+       do {
+               ktime_get_real_ts64(&now);
+       } while (timespec64_compare(&now, &target) < 0);
+}
+
 /*
  * IBM ThinkPad R40e crashes mysteriously when going into C2 or C3.
  * For now disable this. Probably a bug somewhere else.
@@ -660,8 +674,12 @@ static void __cpuidle acpi_idle_do_entry(struct 
acpi_processor_cx *cx)
                inb(cx->address);
                /* Dummy wait op - must do something useless after P_LVL2 read
                   because chipsets cannot guarantee that STPCLK# signal
-                  gets asserted in time to freeze execution properly. */
-               inl(acpi_gbl_FADT.xpm_timer_block.address);
+                  gets asserted in time to freeze execution properly.
+
+                  Previously, we do io port access here which could trigger
+                  unnecessary trap to HV for virtualization env. We use dead
+                  loop here to avoid the impact to virtualization env. */
+               dummy_wait();
        }
 }
 
@@ -683,7 +701,7 @@ static int acpi_idle_play_dead(struct cpuidle_device *dev, 
int index)
                else if (cx->entry_method == ACPI_CSTATE_SYSTEMIO) {
                        inb(cx->address);
                        /* See comment in acpi_idle_do_entry() */
-                       inl(acpi_gbl_FADT.xpm_timer_block.address);
+                       dummy_wait();
                } else
                        return -ENODEV;
        }
@@ -902,6 +920,7 @@ static inline void 
acpi_processor_cstate_first_run_checks(void)
 {
        acpi_status status;
        static int first_run;
+       struct timespec64 ts0, ts1;
 
        if (first_run)
                return;
@@ -912,6 +931,13 @@ static inline void 
acpi_processor_cstate_first_run_checks(void)
                          max_cstate);
        first_run++;
 
+       /* profiling the time used for dummy wait op */
+       ktime_get_real_ts64(&ts0);
+       inl(acpi_gbl_FADT.xpm_timer_block.address);
+       ktime_get_real_ts64(&ts1);
+
+       dummy_delta = timespec64_sub(ts1, ts0);
+
        if (acpi_gbl_FADT.cst_control && !nocst) {
                status = acpi_os_write_port(acpi_gbl_FADT.smi_command,
                                            acpi_gbl_FADT.cst_control, 8);
@@ -920,6 +946,7 @@ static inline void 
acpi_processor_cstate_first_run_checks(void)
                                        "Notifying BIOS of _CST ability 
failed"));
        }
 }
+
 #else
 
 static inline int disabled_by_idle_boot_param(void) { return 0; }
-- 
2.19.1