From: Vitaly Kuznetsov <vkuznets@redhat.com>
Subject: Re: [PATCH v2 4/7] x86/hyper-v: redirect reenlightment notifications
 on CPU offlining
Date: Mon, 15 Jan 2018 11:44:12 +0100
Message-ID: <87y3kziepv.fsf@vitty.brq.redhat.com>
References: <20171213150945.24054-1-vkuznets@redhat.com>
 <20171213150945.24054-5-vkuznets@redhat.com>
 <alpine.DEB.2.20.1801142142280.2371@nanos>
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Cc: Stephen Hemminger <sthemmin@microsoft.com>, kvm@vger.kernel.org,
 Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
 Haiyang Zhang <haiyangz@microsoft.com>, x86@kernel.org,
 linux-kernel@vger.kernel.org, devel@linuxdriverproject.org,
 "Michael Kelley \(EOSG\)" <Michael.H.Kelley@microsoft.com>,
 Ingo Molnar <mingo@redhat.com>, Roman Kagan <rkagan@virtuozzo.com>,
 Andy Lutomirski <luto@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
 Paolo Bonzini <pbonzini@redhat.com>, Mohammed Gamal <mmorsy@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
In-Reply-To: <alpine.DEB.2.20.1801142142280.2371@nanos> (Thomas Gleixner's
 message of "Sun, 14 Jan 2018 21:44:38 +0100 (CET)")
Errors-To: driverdev-devel-bounces@linuxdriverproject.org
Sender: "devel" <driverdev-devel-bounces@linuxdriverproject.org>

Thomas Gleixner <tglx@linutronix.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