Re: [RFC v2 PATCH 2/7] KVM: Track the pid of the VM process

[Punit Agrawal]

Hi Christoffer,

Christoffer Dall <christoffer.dall@xxxxxxxxxx> writes:

> On Mon, Sep 05, 2016 at 05:31:32PM +0100, Punit Agrawal wrote:
>> Userspace tools such as perf can be used to profile individual
>> processes.
>> 
>> Track the PID of the virtual machine process to match profiling requests
>> targeted at it. This can be used to take appropriate action to enable
>> the requested profiling operations for the VMs of interest.
>> 
>> Signed-off-by: Punit Agrawal <punit.agrawal@xxxxxxx>
>> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>> Cc: "Radim KrÄmÃÅ" <rkrcmar@xxxxxxxxxx>
>> Cc: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
>> Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
>> ---
>>  include/linux/kvm_host.h | 1 +
>>  virt/kvm/kvm_main.c      | 2 ++
>>  2 files changed, 3 insertions(+)
>> 
>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
>> index 9c28b4d..7c42c94 100644
>> --- a/include/linux/kvm_host.h
>> +++ b/include/linux/kvm_host.h
>> @@ -374,6 +374,7 @@ struct kvm_memslots {
>>  struct kvm {
>>  	spinlock_t mmu_lock;
>>  	struct mutex slots_lock;
>> +	struct pid *pid;
>>  	struct mm_struct *mm; /* userspace tied to this vm */
>>  	struct kvm_memslots *memslots[KVM_ADDRESS_SPACE_NUM];
>>  	struct srcu_struct srcu;
>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>> index 1950782..ab2535a 100644
>> --- a/virt/kvm/kvm_main.c
>> +++ b/virt/kvm/kvm_main.c
>> @@ -613,6 +613,7 @@ static struct kvm *kvm_create_vm(unsigned long type)
>>  	spin_lock_init(&kvm->mmu_lock);
>>  	atomic_inc(&current->mm->mm_count);
>>  	kvm->mm = current->mm;
>> +	kvm->pid = get_task_pid(current, PIDTYPE_PID);
>
> How dooes this deal with threading?  Is the idea that the user by
> specifying the main thread's pid will enable trapping for all vcpu
> threads belonging to that VM?

Yes that's correct - specifying the main thread PID will enable trapping
for the VM (all vcpus).

I am happy to move to a more suitable identifier if available.

Thanks,
Punit

>
>>  	kvm_eventfd_init(kvm);
>>  	mutex_init(&kvm->lock);
>>  	mutex_init(&kvm->irq_lock);
>> @@ -712,6 +713,7 @@ static void kvm_destroy_vm(struct kvm *kvm)
>>  	int i;
>>  	struct mm_struct *mm = kvm->mm;
>>  
>> +	put_pid(kvm->pid);
>>  	kvm_destroy_vm_debugfs(kvm);
>>  	kvm_arch_sync_events(kvm);
>>  	spin_lock(&kvm_lock);
>> -- 
>> 2.8.1
>> 
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