From: Thomas Gleixner 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 --- 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;