From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755292AbcIFLIj convert rfc822-to-8bit (ORCPT ); Tue, 6 Sep 2016 07:08:39 -0400 Received: from fw-tnat.cambridge.arm.com ([217.140.96.140]:58396 "EHLO cam-smtp0.cambridge.arm.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753413AbcIFLIi (ORCPT ); Tue, 6 Sep 2016 07:08:38 -0400 From: Punit Agrawal To: Christoffer Dall Cc: kvm@vger.kernel.org, Marc Zyngier , Will Deacon , linux-kernel@vger.kernel.org, Steven Rostedt , Ingo Molnar , Paolo Bonzini , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Subject: Re: [RFC v2 PATCH 2/7] KVM: Track the pid of the VM process References: <1473093097-30932-1-git-send-email-punit.agrawal@arm.com> <1473093097-30932-3-git-send-email-punit.agrawal@arm.com> <20160906062252.GA30513@cbox> <87poohjqzk.fsf@e105922-lin.cambridge.arm.com> <20160906102542.GG30513@cbox> Date: Tue, 06 Sep 2016 12:07:59 +0100 In-Reply-To: <20160906102542.GG30513@cbox> (Christoffer Dall's message of "Tue, 6 Sep 2016 12:25:42 +0200") Message-ID: <877fapjng0.fsf@e105922-lin.cambridge.arm.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Christoffer Dall writes: > On Tue, Sep 06, 2016 at 10:51:27AM +0100, Punit Agrawal wrote: >> Hi Christoffer, >> >> Christoffer Dall 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 >> >> Cc: Paolo Bonzini >> >> Cc: "Radim Krčmář" >> >> Cc: Christoffer Dall >> >> Cc: Marc Zyngier >> >> --- >> >> 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(¤t->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. >> > > What is the 'main thread' ? > > Does something mandate that the VM is created by the thread group > leader? If not, is it not a bit strange from a user perspective, that > you have to find the specific subthread pid that created the vm to > enable this tracing for all vcpu threads and that the tgid doesn't work > in this case? Let me correct my terminology usage - the value recorded above (and used to identify the VM) should be the tgid. It is confusing because 'ps' reports it as pid. I picked the value as existing KVM code already uses the PID of the creating task (see kvm_create_vm_debugfs) to export VM statistics in debugfs. If I've got this wrong, then kvm_create_vm_debugfs also likely needs an update. What do you think? > > Thanks, > -Christoffer > _______________________________________________ > kvmarm mailing list > kvmarm@lists.cs.columbia.edu > https://lists.cs.columbia.edu/mailman/listinfo/kvmarm