Re: [PATCH 1/2] x86: notify hypervisor about guest entering s2idle state

[Limonciello, Mario]

On 6/16/2022 11:48, Sean Christopherson wrote:
> On Wed, Jun 15, 2022, Grzegorz Jaszczyk wrote:
> > pt., 10 cze 2022 o 16:30 Sean Christopherson <seanjc@xxxxxxxxxx> napisał(a):
> > > MMIO or PIO for the actual exit, there's nothing special about hypercalls.  As for
> > > enumerating to the guest that it should do something, why not add a new ACPI_LPS0_*
> > > function?  E.g. something like
> > >
> > > static void s2idle_hypervisor_notify(void)
> > > {
> > >          if (lps0_dsm_func_mask > 0)
> > >                  acpi_sleep_run_lps0_dsm(ACPI_LPS0_EXIT_HYPERVISOR_NOTIFY
> > >                                          lps0_dsm_func_mask, lps0_dsm_guid);
> > > }
> >
> > Great, thank you for your suggestion! I will try this approach and
> > come back. Since this will be the main change in the next version,
> > will it be ok for you to add Suggested-by: Sean Christopherson
> > <seanjc@xxxxxxxxxx> tag?
>
> If you want, but there's certainly no need to do so.  But I assume you or someone
> at Intel will need to get formal approval for adding another ACPI LPS0 function?
> I.e. isn't there work to be done outside of the kernel before any patches can be
> merged?

There are 3 different LPS0 GUIDs in use.  An Intel one, an AMD (legacy) 
one, and a Microsoft one.  They all have their own specs, and so if this 
was to be added I think all 3 need to be updated.

As this is Linux specific hypervisor behavior, I don't know you would be 
able to convince Microsoft to update theirs' either.

How about using s2idle_devops?  There is a prepare() call and a 
restore() call that is set for each handler.  The only consumer of this 
ATM I'm aware of is the amd-pmc driver, but it's done like a 
notification chain so that a bunch of drivers can hook in if they need to.

Then you can have this notification path and the associated ACPI device 
it calls out to be it's own driver.