linux-kernel - Re: [PART1 RFC v3 02/12] KVM: x86: Introducing kvm_x86

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Date:	Wed, 30 Mar 2016 19:18:14 +0700
From:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
To:	Paolo Bonzini <pbonzini@...hat.com>, <rkrcmar@...hat.com>,
	<joro@...tes.org>, <bp@...en8.de>, <gleb@...nel.org>,
	<alex.williamson@...hat.com>
CC:	<kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<wei@...hat.com>, <sherry.hurwitz@....com>
Subject: Re: [PART1 RFC v3 02/12] KVM: x86: Introducing kvm_x86_ops VM
 init/uninit hooks

Hi Paolo,

On 3/30/16 19:07, Paolo Bonzini wrote:
>
>
> On 30/03/2016 12:00, Suravee Suthikulpanit wrote:
>> Hi Paolo,
>>
>> On 3/29/16 18:47, Suravee Suthikulpanit wrote:
>>> Hi,
>>>
>>> On 03/29/2016 05:21 PM, Paolo Bonzini wrote:
>>>>
>>>>
>>>> On 29/03/2016 07:27, Suravee Suthikulpanit wrote:
>>>>>>
>>>>>>>> Adding function pointers in struct kvm_x86_ops for
>>>>>>>> processor-specific
>>>>>>>> layer to provide hooks for when KVM initialize and un-initialize VM.
>>>>>> This is not the only thing your patch is doing, and the "other" change
>>>>>> definitely needs a lot more explanation about why you did it and how
>>>>>> you
>>>>>> audited the code to ensure that it is safe.
>>>>>>
>>>>>> Paolo
>>>>>>
>>>>>
>>>>> Sorry, for not mentioning this earlier. I am moving the
>>>>> kvm_arch_init_vm() call mainly to go after mutex_init(&kvm->slots_lock)
>>>>> since I am calling the x86_set_memory_region() (which uses slots_lock)
>>>>> in the vm_init() hooks (for AVIC initialization).
>>>>>
>>>>> Lemme re-check if this would be safe for other code.
>>>>
>>>> No problem.  In the meanwhile a patch got in ("KVM: fix spin_lock_init
>>>> order on x86") that should help you.
>>>>
>>>> Thanks,
>>>>
>>>> Paolo
>>>>
>>>
>>> Right.... that's just what I need :) I'll re-base to the latest tip then.
>>
>> Actually, in the file virt/kvm/kvm_main.c, I still need to move the
>> kvm_arch_init_vm() to some place after the call to kvm_alloc_memslots()
>> since I am calling x86_set_memory_region() in the vm_init hook.
>>
>>          r = -ENOMEM;
>>          for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
>>                  kvm->memslots[i] = kvm_alloc_memslots();
>>                  if (!kvm->memslots[i])
>>                          goto out_err_no_srcu;
>>          }
>>
>>          if (init_srcu_struct(&kvm->srcu))
>>                  goto out_err_no_srcu;
>>          if (init_srcu_struct(&kvm->irq_srcu))
>>                  goto out_err_no_irq_srcu;
>>          for (i = 0; i < KVM_NR_BUSES; i++) {
>>                  kvm->buses[i] = kzalloc(sizeof(struct kvm_io_bus),
>>                                          GFP_KERNEL);
>>                  if (!kvm->buses[i])
>>                          goto out_err;
>>          }
>> //HERE
>>          r = kvm_arch_init_vm(kvm, type);
>>          if (r)
>>                  goto out_err;
>>
>> Do you think that would be a problem?
>
> Can you delay that to after the creation of the first VCPU?

Sure, I can. That's what I was doing originally before we introduce the 
vm_init hook. I just thought that this would make a nice place.

> Allocating AVIC data structures is not required if userspace has not
> called KVM_CREATE_IRQCHIP or enabled KVM_CAP_SPLIT_IRQCHIP.
>
> Paolo
>

Okay.

Thanks,
Suravee