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

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Message-ID: <87y3kziepv.fsf@vitty.brq.redhat.com>
Date:   Mon, 15 Jan 2018 11:44:12 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
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

Thomas Gleixner <tglx@...utronix.de> writes:

> 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...
>

Yes, someone around made a comment 'what happens if some day we'll have
parallel cpu hot[un]plug' and I added this. Not really needed, will drop
in v3.

>> +	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?
>

Cool, thanks)

-- 
  Vitaly