[PATCH] x86: kvm Require const tsc for RT

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

From: Thomas Gleixner <tglx@linutronix.de>
Date: Sun, 6 Nov 2011 12:26:18 +0100

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>
---
 arch/x86/kvm/x86.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 82a9dcd8c67fe..54d2090d04e7a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8826,6 +8826,12 @@ 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();
-- 
2.35.1