On Wed, Oct 23, 2019 at 10:45 AM David Laight <David.Laight@xxxxxxxxxx> wrote:
>
> 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().
I was about to make a similar comment.
