From: Yin Fengwei
> Sent: 23 October 2019 08:50
> In function acpi_idle_do_entry(), an ioport access is used for dummy
> wait to guarantee hardware behavior. But it could trigger unnecessary
> vmexit if kernel is running as guest in virtualization environtment.
>
> If it's in virtualization environment, the deeper C state enter
> operation (inb()) will trap to hyervisor. It's not needed to do
> dummy wait after the inb() call. So we remove the dummy io port
> access to avoid unnecessary VMexit.
>
> We keep dummy io port access to maintain timing for native environment.
>
> Signed-off-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
> ---
> ChangeLog:
> v2 -> v3:
> - Remove dummy io port access totally for virtualization env.
>
> v1 -> v2:
> - Use ndelay instead of dead loop for dummy delay.
>
> drivers/acpi/processor_idle.c | 36 ++++++++++++++++++++++++++++++++---
> 1 file changed, 33 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> index ed56c6d20b08..0c4a97dd6917 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -58,6 +58,17 @@ struct cpuidle_driver acpi_idle_driver = {
> static
> DEFINE_PER_CPU(struct acpi_processor_cx * [CPUIDLE_STATE_MAX], acpi_cstate);
>
> +static void (*dummy_wait)(u64 address);
> +
> +static void default_dummy_wait(u64 address)
> +{
> + inl(address);
> +}
> +
> +static void default_noop_wait(u64 address)
> +{
> +}
> +
Overengineered...
Just add:
static void wait_for_freeze(void)
{
#ifdef CONFIG_X86
/* No delay is needed if we are a guest */
if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
return;
#endif
/* 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);
}
and use it to replace the inl().
...
> +#ifdef CONFIG_X86
> + /* For x86, if we are running in guest, we don't need extra
> + * access ioport as dummy wait.
> + */
> + if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
> + pr_err("We are in virtual env");
> + dummy_wait = default_noop_wait;
> + } else {
> + pr_err("We are not in virtual env");
> + }
> +#endif
WTF are the pr_err() for???
David
-
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