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Date:   Thu, 16 Jun 2022 11:58:42 -0500
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Subject: Re: [PATCH 1/2] x86: notify hypervisor about guest entering s2idle
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To:     Sean Christopherson <seanjc@google.com>,
        Grzegorz Jaszczyk <jaz@semihalf.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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        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
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        Hans de Goede <hdegoede@redhat.com>,
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From:   "Limonciello, Mario" <mario.limonciello@amd.com>
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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> 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@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 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.