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

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Date:   Tue, 6 Sep 2016 08:22:52 +0200
From:   Christoffer Dall <christoffer.dall@...aro.org>
To:     Punit Agrawal <punit.agrawal@....com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        Marc Zyngier <marc.zyngier@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [RFC v2 PATCH 2/7] KVM: Track the pid of the VM process

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@....com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: "Radim Krčmář" <rkrcmar@...hat.com>
> Cc: Christoffer Dall <christoffer.dall@...aro.org>
> Cc: Marc Zyngier <marc.zyngier@....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
>