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Subject: x86: kvm Require const tsc for RT
From: Thomas Gleixner <tglx@linutronix.de>
Date: Sun, 06 Nov 2011 12:26:18 +0100
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.4/older/patches-5.4.17-rt8.tar.xz
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 | 8 ++++++++
1 file changed, 8 insertions(+)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7207,6 +7207,14 @@ int kvm_arch_init(void *opaque)
goto out;
}
+#ifdef CONFIG_PREEMPT_RT
+ if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) {
+ pr_err("RT requires X86_FEATURE_CONSTANT_TSC\n");
+ r = -EOPNOTSUPP;
+ goto out;
+ }
+#endif
+
r = -ENOMEM;
x86_fpu_cache = kmem_cache_create("x86_fpu", sizeof(struct fpu),
__alignof__(struct fpu), SLAB_ACCOUNT,
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