linux-kernel - [v2 PATCH 1/4] x86/kvm: Reserve KVM_FEATURE_HOST_SUSPEND_TIME and MSR_KVM_HOST_SUSPEND

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Message-Id: <20210806190607.v2.1.I2a67009253163b8eecf1ae8d050c541d35ac0bd8@changeid>
Date:   Fri,  6 Aug 2021 19:07:07 +0900
From:   Hikaru Nishida <hikalium@...omium.org>
To:     linux-kernel@...r.kernel.org, dme@....org, tglx@...utronix.de,
        mlevitsk@...hat.com
Cc:     suleiman@...gle.com, Hikaru Nishida <hikalium@...omium.org>,
        Jonathan Corbet <corbet@....net>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: [v2 PATCH 1/4] 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   | 30 ++++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/Documentation/virt/kvm/cpuid.rst b/Documentation/virt/kvm/cpuid.rst
index bda3e3e737d7..f17b95b0d943 100644
--- a/Documentation/virt/kvm/cpuid.rst
+++ b/Documentation/virt/kvm/cpuid.rst
@@ -103,6 +103,9 @@ KVM_FEATURE_HC_MAP_GPA_RANGE       16          guest checks this feature bit bef
 KVM_FEATURE_MIGRATION_CONTROL      17          guest checks this feature bit before
                                                using MSR_KVM_MIGRATION_CONTROL
 
+KVM_FEATURE_HOST_SUSPEND_TIME      18          host suspend time information
+                                               is available at msr 0x4b564d09.
+
 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 9315fc385fb0..a218a350d0d0 100644
--- a/Documentation/virt/kvm/msr.rst
+++ b/Documentation/virt/kvm/msr.rst
@@ -389,3 +389,33 @@ data:
         guest is communicating page encryption status to the host using the
         ``KVM_HC_MAP_GPA_RANGE`` hypercall, it can set bit 0 in this MSR to
         allow live migration of the guest.
+
+MSR_KVM_HOST_SUSPEND_TIME:
+	0x4b564d09
+
+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_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. The update will be notified through
+	VIRT_SUSPEND_TIMING_VECTOR IRQ. Fields have the following meanings:
+
+	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 18 in 0x4000001 cpuid
+	leaf prior to usage.
-- 
2.32.0.605.g8dce9f2422-goog