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

Christoffer Dall
2016-09-06T06:20:28Z

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?

> 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
>