linux-kernel - Re: [PATCH v2 4/7] x86/hyper-v: redirect reenlightment notifications on CPU offlining

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Date:   Sun, 14 Jan 2018 21:44:38 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
cc:     kvm@...r.kernel.org, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>,
        Andy Lutomirski <luto@...nel.org>,
        Mohammed Gamal <mmorsy@...hat.com>,
        Cathy Avery <cavery@...hat.com>,
        Roman Kagan <rkagan@...tuozzo.com>,
        linux-kernel@...r.kernel.org, devel@...uxdriverproject.org
Subject: Re: [PATCH v2 4/7] x86/hyper-v: redirect reenlightment notifications
 on CPU offlining

On Wed, 13 Dec 2017, Vitaly Kuznetsov wrote:
> +static int hv_cpu_die(unsigned int cpu)
> +{
> +	struct hv_reenlightenment_control re_ctrl;
> +	int i;
> +	static DEFINE_SPINLOCK(lock);
> +
> +	if (hv_reenlightenment_cb == NULL)
> +		return 0;
> +
> +	/* Make sure the CPU we migrate to is not going away too */
> +	spin_lock(&lock);

What kind of voodoo is this? CPU hotplug is serialized already...

> +	rdmsrl(HV_X64_MSR_REENLIGHTENMENT_CONTROL, *((u64 *)&re_ctrl));
> +	if (re_ctrl.target_vp == hv_vp_index[cpu]) {
> +		/* Find some other online CPU */
> +		for_each_online_cpu(i) {


  		cpu = cpumask_any_but(cpu_online_mask);

Hmm?

Thanks,

	tglx