linux-kernel - Re: [PATCH: kvm 3/5] Fix hotadd of CPUs for KVM.

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Date:	Sun, 27 Sep 2009 15:39:51 -1000
From:	Zachary Amsden <zamsden@...hat.com>
To:	Avi Kivity <avi@...hat.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH: kvm 3/5] Fix hotadd of CPUs for KVM.

On 09/26/2009 10:52 PM, Avi Kivity wrote:
> On 09/25/2009 03:47 AM, Zachary Amsden wrote:
>>
>> --- a/virt/kvm/kvm_main.c
>> +++ b/virt/kvm/kvm_main.c
>> @@ -1716,9 +1716,6 @@ static int kvm_cpu_hotplug(struct 
>> notifier_block *notifier, unsigned long val,
>>   {
>>       int cpu = (long)v;
>>
>> -    if (!kvm_usage_count)
>> -        return NOTIFY_OK;
>> -
>
> Why?  You'll now do hardware_enable() even if kvm is not in use.

Because otherwise you'll never allocate and hardware_enable_all will fail:

Switch to broadcast mode on CPU1
svm_hardware_enable: svm_data is NULL on 1
kvm: enabling virtualization on CPU1 failed
qemu-system-x86[8698]: segfault at 20 ip 00000000004db22f sp 
00007fff0a3b4560 error 6 in qemu-system-x86_64[400000+21f000]

Perhaps I can make this work better by putting the allocation within 
hardware_enable_all.

Zach
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