linux-kernel - Re: [RFC][PATCH 1/5] [PATCH 1/5] kvm: register in task

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Message-ID: <20180904002818.nq2ejxlsn4o34anl@wfg-t540p.sh.intel.com>
Date:   Tue, 4 Sep 2018 08:28:18 +0800
From:   Fengguang Wu <fengguang.wu@...el.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>
Cc:     Nikita Leshenko <nikita.leshchenko@...cle.com>,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        dongx.peng@...el.com, jingqi.liu@...el.com, eddie.dong@...el.com,
        dave.hansen@...el.com, ying.huang@...el.com, bgregg@...flix.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 1/5] [PATCH 1/5] kvm: register in task_struct

Hi Christian and Nikita,

On Mon, Sep 03, 2018 at 06:03:49PM +0200, Christian Borntraeger wrote:
>
>
>On 09/03/2018 04:10 PM, Nikita Leshenko wrote:
>> On September 2, 2018 5:21:15 AM, fengguang.wu@...el.com wrote:
>>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>>> index 8b47507faab5..0c483720de8d 100644
>>> --- a/virt/kvm/kvm_main.c
>>> +++ b/virt/kvm/kvm_main.c
>>> @@ -3892,6 +3892,7 @@ static void kvm_uevent_notify_change(unsigned int type, struct kvm *kvm)
>>>  	if (type == KVM_EVENT_CREATE_VM) {
>>>  		add_uevent_var(env, "EVENT=create");
>>>  		kvm->userspace_pid = task_pid_nr(current);
>>> +		current->kvm = kvm;
>>
>> Is it OK to store `kvm` on the task_struct? What if the thread that
>> originally created the VM exits? From the documentation it seems
>> like a VM is associated with an address space and not a specific
>> thread, so maybe it should be stored on mm_struct?
>
>Yes, ioctls accessing the kvm can happen from all threads.

Good point, thank you for the tips! I'll move kvm pointer to mm_struct.

>> From Documentation/virtual/kvm/api.txt:
>>    Only run VM ioctls from the same process (address space) that was used
>>    to create the VM.
>>
>> -Nikita

Regards,
Fengguang