linux-kernel - [PATCH v6 3/3] KVM: x86: Add "suspendsteal" cmdline to request host to add suspend duration in steal time

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Message-Id: <20250709070450.473297-4-suleiman@google.com>
Date: Wed,  9 Jul 2025 16:04:50 +0900
From: Suleiman Souhlal <suleiman@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, Chao Gao <chao.gao@...el.com>, 
	David Woodhouse <dwmw2@...radead.org>, Sergey Senozhatsky <senozhatsky@...omium.org>, 
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, Tzung-Bi Shih <tzungbi@...nel.org>, 
	John Stultz <jstultz@...gle.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	ssouhlal@...ebsd.org, Suleiman Souhlal <suleiman@...gle.com>
Subject: [PATCH v6 3/3] KVM: x86: Add "suspendsteal" cmdline to request host
 to add suspend duration in steal time

Introduce a new command line parameter, "suspendsteal", enabling the
guest to use MSR_KVM_SUSPEND_STEAL, which tells the host that it would
like host suspend duration to be included in steal time.

Signed-off-by: Suleiman Souhlal <suleiman@...gle.com>
---
 Documentation/admin-guide/kernel-parameters.txt |  5 +++++
 arch/x86/kernel/kvm.c                           | 15 +++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index f1f2c0874da9dd..9f5758ca8fadd5 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -7074,6 +7074,11 @@
 			improve throughput, but will also increase the
 			amount of memory reserved for use by the client.
 
+	suspendsteal
+			[X86,PV_OPS]
+			Enable requesting the host to include the duration the
+			host was suspended in steal time. Disabled by default.
+
 	suspend.pm_test_delay=
 			[SUSPEND]
 			Sets the number of seconds to remain in a suspend test
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 921c1c783bc187..35d1bb2283c2c0 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -320,6 +320,18 @@ static void __init paravirt_ops_setup(void)
 #endif
 }
 
+static bool suspend_steal;
+
+static int __init suspendsteal_setup(char *s)
+{
+	if (kvm_para_has_feature(KVM_FEATURE_SUSPEND_STEAL))
+		suspend_steal = true;
+
+	return 0;
+}
+
+early_param("suspendsteal", suspendsteal_setup);
+
 static void kvm_register_steal_time(void)
 {
 	int cpu = smp_processor_id();
@@ -331,6 +343,9 @@ static void kvm_register_steal_time(void)
 	wrmsrq(MSR_KVM_STEAL_TIME, (slow_virt_to_phys(st) | KVM_MSR_ENABLED));
 	pr_debug("stealtime: cpu %d, msr %llx\n", cpu,
 		(unsigned long long) slow_virt_to_phys(st));
+
+	if (suspend_steal)
+		wrmsrl(MSR_KVM_SUSPEND_STEAL, KVM_MSR_ENABLED);
 }
 
 static DEFINE_PER_CPU_DECRYPTED(unsigned long, kvm_apic_eoi) = KVM_PV_EOI_DISABLED;
-- 
2.50.0.727.gbf7dc18ff4-goog