Re: [PATCH] x86: kvm Require const tsc for RT

[Paolo Bonzini <pbonzini@redhat.com>]

On 3/1/22 18:55, Sebastian Andrzej Siewior wrote:
> 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();

Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Thanks,

Paolo