linux-kernel - Re: [RFC PATCH 1/6] x86/kvm: Reserve KVM_FEATURE_HOST_SUSPEND_TIME and MSR_KVM_HOST_SUSPEND

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Message-ID: <cunk0onkbgt.fsf@dme.org>
Date:   Tue, 27 Apr 2021 16:12:50 +0100
From:   David Edmondson <dme@....org>
To:     Hikaru Nishida <hikalium@...omium.org>, kvm@...r.kernel.org
Cc:     suleiman@...gle.com, Hikaru Nishida <hikalium@...omium.org>,
        Jonathan Corbet <corbet@....net>,
        Paolo Bonzini <pbonzini@...hat.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/6] x86/kvm: Reserve KVM_FEATURE_HOST_SUSPEND_TIME
 and MSR_KVM_HOST_SUSPEND_TIME

On Monday, 2021-04-26 at 18:06:40 +09, Hikaru Nishida wrote:

> No functional change; just add documentation for
> KVM_FEATURE_HOST_SUSPEND_TIME and its corresponding
> MSR_KVM_HOST_SUSPEND_TIME to support virtual suspend timing injection in
> later patches.
>
> Signed-off-by: Hikaru Nishida <hikalium@...omium.org>
> ---
>
>  Documentation/virt/kvm/cpuid.rst |  3 +++
>  Documentation/virt/kvm/msr.rst   | 29 +++++++++++++++++++++++++++++
>  2 files changed, 32 insertions(+)
>
> diff --git a/Documentation/virt/kvm/cpuid.rst b/Documentation/virt/kvm/cpuid.rst
> index cf62162d4be2..c7cb581b9a9b 100644
> --- a/Documentation/virt/kvm/cpuid.rst
> +++ b/Documentation/virt/kvm/cpuid.rst
> @@ -96,6 +96,9 @@ KVM_FEATURE_MSI_EXT_DEST_ID        15          guest checks this feature bit
>                                                 before using extended destination
>                                                 ID bits in MSI address bits 11-5.
>  
> +KVM_FEATURE_HOST_SUSPEND_TIME      16          host suspend time information
> +                                               is available at msr 0x4b564d08.
> +
>  KVM_FEATURE_CLOCKSOURCE_STABLE_BIT 24          host will warn if no guest-side
>                                                 per-cpu warps are expected in
>                                                 kvmclock
> diff --git a/Documentation/virt/kvm/msr.rst b/Documentation/virt/kvm/msr.rst
> index e37a14c323d2..de96743245c9 100644
> --- a/Documentation/virt/kvm/msr.rst
> +++ b/Documentation/virt/kvm/msr.rst
> @@ -376,3 +376,32 @@ data:
>  	write '1' to bit 0 of the MSR, this causes the host to re-scan its queue
>  	and check if there are more notifications pending. The MSR is available
>  	if KVM_FEATURE_ASYNC_PF_INT is present in CPUID.
> +
> +MSR_KVM_HOST_SUSPEND_TIME:
> +	0x4b564d08
> +
> +data:
> +	8-byte alignment physical address of a memory area which must be
> +	in guest RAM, plus an enable bit in bit 0. This memory is expected to
> +	hold a copy of the following structure::
> +
> +	 struct kvm_host_suspend_time {
> +		__u64   suspend_time_ns;
> +	 };
> +
> +	whose data will be filled in by the hypervisor.
> +	If the guest register this structure through the MSR write, the host
> +	will stop all the clocks including TSCs observed by the guest during
> +	the host's suspension and report the duration of suspend through this
> +	structure. Fields have the following meanings:
> +
> +	host_suspend_time_ns:

s/host_suspend_time_ns/suspend_time_ns/

> +		Total number of nanoseconds passed during the host's suspend
> +		while the VM is running. This value will be increasing
> +		monotonically.
> +
> +	Note that although MSRs are per-CPU entities, the effect of this
> +	particular MSR is global.
> +
> +	Availability of this MSR must be checked via bit 16 in 0x4000001 cpuid
> +	leaf prior to usage.
> -- 
> 2.31.1.498.g6c1eba8ee3d-goog

dme.
-- 
I do believe it's Madame Joy.