From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@redhat.com>
Subject: Re: [PATCH] Activate Virtualization On Demand v2
Date: Tue, 16 Jun 2009 17:01:01 +0300
Message-ID: <4A37A59D.5070604@redhat.com>
References: <1245065405-5714-1-git-send-email-agraf@suse.de>
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Cc: kvm@vger.kernel.org
To: Alexander Graf <agraf@suse.de>
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On 06/15/2009 02:30 PM, Alexander Graf wrote:
> X86 CPUs need to have some magic happening to enable the virtualization
> extensions on them. This magic can result in unpleasant results for
> users, like blocking other VMMs from working (vmx) or using invalid TLB
> entries (svm).
>
> Currently KVM activates virtualization when the respective kernel module
> is loaded. This blocks us from autoloading KVM modules without breaking
> other VMMs.
>
> To circumvent this problem at least a bit, this patch introduces on
> demand activation of virtualization. This means, that instead
> virtualization is enabled on creation of the first virtual machine
> and disabled on destruction of the last one.
>
> So using this, KVM can be easily autoloaded, while keeping other
> hypervisors usable.
>
> +static int hardware_enable_all(void)
> +{
> +	int r = 0;
> +
> +	spin_lock(&kvm_lock);
> +
> +	kvm_usage_count++;
> +	if (kvm_usage_count == 1) {
> +		atomic_set(&hardware_enable_failed, 1);
> +		on_each_cpu(hardware_enable, NULL, 1);
> +
> +		if (!atomic_dec_and_test(&hardware_enable_failed))
> +			r = -EBUSY;
> +	}
>    

That's a little obfuscated.  I suggest atomic_set(..., p) and 
atomic_read(...).

> +
>   static int kvm_cpu_hotplug(struct notifier_block *notifier, unsigned long val,
>   			   void *v)
>   {
>   	int cpu = (long)v;
>
> +	if (!kvm_usage_count)
> +		return NOTIFY_OK;
> +
>   	val&= ~CPU_TASKS_FROZEN;
>   	switch (val) {
>   	case CPU_DYING:
> @@ -2513,13 +2571,15 @@ static void kvm_exit_debug(void)
>
>   static int kvm_suspend(struct sys_device *dev, pm_message_t state)
>   {
> -	hardware_disable(NULL);
> +	if (kvm_usage_count)
> +		hardware_disable(NULL);
>   	return 0;
>   }
>
>   static int kvm_resume(struct sys_device *dev)
>   {
> -	hardware_enable(NULL);
> +	if (kvm_usage_count)
> +		hardware_enable(NULL);
>   	return 0;
>   }
>
>    

Please tell me you tested suspend/resume with/without VMs and cpu 
hotunplug/hotplug.


-- 
error compiling committee.c: too many arguments to function