From: Thomas Gleixner <tglx@linutronix.de>
Date: Sun, 6 Nov 2011 11:26:18 +0000 (+0100)
Subject: kvm: x86: Require const tsc for RT
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=5e17b2ee45b941fb7bc46107810d727088be392e;p=linux.git

kvm: x86: Require const tsc for RT

Non constant TSC is a nightmare on bare metal already, but with
virtualization it becomes a complete disaster because the workarounds
are horrible latency wise. That's also a preliminary for running RT in
a guest on top of a RT host.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Message-Id: <Yh5eJSG19S2sjZfy@linutronix.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4fa4d8269e5b3..c58265d9f1b23 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8865,6 +8865,12 @@ int kvm_arch_init(void *opaque)
 		goto out;
 	}
 
+	if (IS_ENABLED(CONFIG_PREEMPT_RT) && !boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) {
+		pr_err("RT requires X86_FEATURE_CONSTANT_TSC\n");
+		r = -EOPNOTSUPP;
+		goto out;
+	}
+
 	r = -ENOMEM;
 
 	x86_emulator_cache = kvm_alloc_emulator_cache();