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From:   Grzegorz Jaszczyk <jaz@semihalf.com>
Date:   Mon, 20 Jun 2022 17:43:59 +0200
Message-ID: <CAH76GKP=2wu4+eqLCFu1F5a4rHhReUT_7N89K8xbO-gSqEQ-3w@mail.gmail.com>
Subject: Re: [PATCH 1/2] x86: notify hypervisor about guest entering s2idle state
To:     "Limonciello, Mario" <mario.limonciello@amd.com>,
        Sean Christopherson <seanjc@google.com>
Cc:     linux-kernel@vger.kernel.org, Dmytro Maluka <dmy@semihalf.com>,
        Zide Chen <zide.chen@intel.corp-partner.google.com>,
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czw., 16 cze 2022 o 18:58 Limonciello, Mario
<mario.limonciello@amd.com> napisa=C5=82(a):
>
> 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@google.com> napis=
a=C5=82(a):
> >>> MMIO or PIO for the actual exit, there's nothing special about hyperc=
alls.  As for
> >>> enumerating to the guest that it should do something, why not add a n=
ew 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_NO=
TIFY
> >>>                                          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@google.com> 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 patch=
es 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.

Yes this will not be easy to achieve I think.

>
> 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.

Thank you for your suggestion, just to be sure that I've understand
your idea correctly:
1) it will require to extend acpi_s2idle_dev_ops about something like
hypervisor_notify() call, since existing prepare() is called from end
of acpi_s2idle_prepare_late so it is too early as it was described in
one of previous message (between acpi_s2idle_prepare_late and place
where we use hypercall there are several places where the suspend
could be canceled, otherwise we could probably try to trap on other
acpi_sleep_run_lps0_dsm occurrence from acpi_s2idle_prepare_late).

2) using newly introduced acpi_s2idle_dev_ops hypervisor_notify() call
will allow to register handler from Intel x86/intel/pmc/core.c driver
and/or AMD x86/amd-pmc.c driver. Therefore we will need to get only
Intel and/or AMD approval about extending the ACPI LPS0 _DSM method,
correct?

I wonder if this will be affordable so just re-thinking loudly if
there is no other mechanism that could be suggested and used upstream
so we could notify hypervisor/vmm about guest entering s2idle state?
Especially that such _DSM function will be introduced only to trap on
some fake MMIO/PIO access and will be useful only for guest ACPI
tables?

Thank you,
Grzegorz