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From: Thomas Gleixner <tglx@linutronix.de>
Date: Sun, 6 Nov 2011 12:26:18 +0100
Subject: [PATCH 090/342] x86: kvm Require const tsc for RT
Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=6a78a1abd53560fa236781a743b6991f1d2115c5
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>
---
arch/x86/kvm/x86.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index be4697d91bb2..11391b7ace1e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6879,6 +6879,13 @@ int kvm_arch_init(void *opaque)
goto out;
}
+#ifdef CONFIG_PREEMPT_RT_FULL
+ if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) {
+ printk(KERN_ERR "RT requires X86_FEATURE_CONSTANT_TSC\n");
+ return -EOPNOTSUPP;
+ }
+#endif
+
r = kvm_mmu_module_init();
if (r)
goto out_free_percpu;
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