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

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Date:	Wed, 30 Mar 2016 17:00:03 +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 3/29/16 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?

Thanks,
Suravee