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

Punit Agrawal
2016-09-06T09:52:06Z

Hi Christoffer,

Christoffer Dall <christoffer.dall@linaro.org> 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@arm.com>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Cc: "Radim Krčmář" <rkrcmar@redhat.com>
>> Cc: Christoffer Dall <christoffer.dall@linaro.org>
>> Cc: Marc Zyngier <marc.zyngier@arm.com>
>> ---
>> 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
>>
> _______________________________________________
> kvmarm mailing list
> kvmarm@lists.cs.columbia.edu
> https://lists.cs.columbia.edu/mailman/listinfo/kvmarm