Date:   Thu, 9 Feb 2023 21:26:33 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Grzegorz Jaszczyk <jaz@semihalf.com>
Cc:     linux-kernel@vger.kernel.org, rafael@kernel.org, dmy@semihalf.com,
        tn@semihalf.com, dbehr@google.com,
        zide.chen@intel.corp-partner.google.com, upstream@semihalf.com,
        hdegoede@redhat.com, markgross@kernel.org, dtor@google.com,
        mario.limonciello@amd.com, linux-pm@vger.kernel.org,
        x86@kernel.org, platform-driver-x86@vger.kernel.org
Subject: Re: [RESEND RFCv2 1/1] platform/x86: Add virtual PMC driver used for
 S2Idle
Message-ID: <Y+VlCWwn35ECE9iz@google.com>
References: <20230209152123.3186930-1-jaz@semihalf.com>
 <20230209152123.3186930-2-jaz@semihalf.com>
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On Thu, Feb 09, 2023, Grzegorz Jaszczyk wrote:
> Virtual PMC driver is meant for the guest VMs for the S2Idle
> notification. Its purpose is to register S2Idle dev ops check handler,
> which will evaluate ACPI _DSM just before the guest enters S2Idle power
> state.
> 
> This allows to trap on MMIO access done as a consequence of _DSM
> evaluation and therefore notify the VMM about the guest entering S2Idle
> state.
> 
> Signed-off-by: Grzegorz Jaszczyk <jaz@semihalf.com>
> ---
> Changelog v1..v2:
> - Take advantage of acpi_s2idle_dev_ops's check() instead of notify()
> ---
>  drivers/platform/x86/Kconfig    |  7 ++++
>  drivers/platform/x86/Makefile   |  3 ++
>  drivers/platform/x86/virt_pmc.c | 73 +++++++++++++++++++++++++++++++++
>  3 files changed, 83 insertions(+)
>  create mode 100644 drivers/platform/x86/virt_pmc.c
> 
> diff --git a/drivers/platform/x86/Kconfig b/drivers/platform/x86/Kconfig
> index 5692385e2d26..b7c3f98031d7 100644
> --- a/drivers/platform/x86/Kconfig
> +++ b/drivers/platform/x86/Kconfig
> @@ -1099,6 +1099,13 @@ config WINMATE_FM07_KEYS
>  	  buttons below the display. This module adds an input device
>  	  that delivers key events when these buttons are pressed.
>  
> +config VIRT_PMC
> +	tristate "Virt PMC"

Maybe spell out "Virtual Power Management Controller"?  See below.

> +	depends on ACPI && SUSPEND

I think it makes sense to take a dependency on HYPERVISOR_GUEST.  It's not strictly
required, but taking that dependency helps clarify that this is a guest-side thing,
e.g. "virtual PMC" in KVM-land means "virtual performance monitoring counter".

And IMO, disabling HYPERVISOR_GUEST should disable these type of guest-specific
features.