linux-kernel - Re: [patch 3/3] KVM: x86: frequency change hypercalls

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Date:   Thu, 2 Feb 2017 16:01:38 -0200
From:   Marcelo Tosatti <mtosatti@...hat.com>
To:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [patch 3/3] KVM: x86: frequency change hypercalls

On Thu, Feb 02, 2017 at 03:47:58PM -0200, Marcelo Tosatti wrote:
> Implement min/max/up/down frequency change 
> KVM hypercalls. To be used by DPDK implementation.
> 
> Also allow such hypercalls from guest userspace.
> 
> Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>
> 
> ---
>  Documentation/virtual/kvm/hypercalls.txt |   45 +++++++++++++++++++
>  arch/x86/kvm/x86.c                       |   71 ++++++++++++++++++++++++++++++-
>  include/uapi/linux/kvm_para.h            |    5 ++
>  3 files changed, 120 insertions(+), 1 deletion(-)
> 
> Index: kvm-pvfreq/arch/x86/kvm/x86.c
> ===================================================================
> --- kvm-pvfreq.orig/arch/x86/kvm/x86.c	2017-02-02 11:17:17.063756725 -0200
> +++ kvm-pvfreq/arch/x86/kvm/x86.c	2017-02-02 11:17:17.822752510 -0200
> @@ -6219,10 +6219,58 @@
>  	kvm_x86_ops->refresh_apicv_exec_ctrl(vcpu);
>  }
>  
> +#ifdef CONFIG_CPU_FREQ_GOV_USERSPACE
> +/* call into cpufreq-userspace governor */
> +static int kvm_pvfreq_up(struct kvm_vcpu *vcpu)
> +{
> +	int ret;
> +	int cpu = get_cpu();
> +
> +	ret = cpufreq_userspace_freq_up(cpu);
> +	put_cpu();
> +
> +	return ret;
> +}
> +
> +static int kvm_pvfreq_down(struct kvm_vcpu *vcpu)
> +{
> +	int ret;
> +	int cpu = get_cpu();
> +
> +	ret = cpufreq_userspace_freq_down(cpu);
> +	put_cpu();
> +
> +	return ret;
> +}
> +
> +static int kvm_pvfreq_max(struct kvm_vcpu *vcpu)
> +{
> +	int ret;
> +	int cpu = get_cpu();
> +
> +	ret = cpufreq_userspace_freq_max(cpu);
> +	put_cpu();
> +
> +	return ret;
> +}
> +
> +static int kvm_pvfreq_min(struct kvm_vcpu *vcpu)
> +{
> +	int ret;
> +	int cpu = get_cpu();
> +
> +	ret = cpufreq_userspace_freq_min(cpu);
> +	put_cpu();
> +
> +	return ret;
> +}
> +#endif
> +
>  int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
>  {
>  	unsigned long nr, a0, a1, a2, a3, ret;
>  	int op_64_bit, r;
> +	bool cpl_check;
>  
>  	r = kvm_skip_emulated_instruction(vcpu);
>  
> @@ -6246,7 +6294,13 @@
>  		a3 &= 0xFFFFFFFF;
>  	}
>  
> -	if (kvm_x86_ops->get_cpl(vcpu) != 0) {
> +	cpl_check = true;
> +	if (nr == KVM_HC_FREQ_UP || nr == KVM_HC_FREQ_DOWN ||
> +	    nr == KVM_HC_FREQ_MIN || nr == KVM_HC_FREQ_MAX)
> +		if (vcpu->arch.allow_freq_hypercall == true)
> +			cpl_check = false;
> +
> +	if (cpl_check == true && kvm_x86_ops->get_cpl(vcpu) != 0) {
>  		ret = -KVM_EPERM;
>  		goto out;

This should fail with EPERM if vcpu->arch.allow_freq_hypercall ==
false, independently of CPL level.

Will resend with that (and other comments) in v2.