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

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Date:   Mon, 26 Apr 2021 18:06:40 +0900
From:   Hikaru Nishida <hikalium@...omium.org>
To:     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: [RFC PATCH 1/6] x86/kvm: Reserve KVM_FEATURE_HOST_SUSPEND_TIME and MSR_KVM_HOST_SUSPEND_TIME

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:
+		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