Re: [PATCH v3] kvm: make vcpu life cycle separated from kvm instance

[Gleb Natapov <gleb@redhat.com>]

On Thu, Dec 15, 2011 at 11:21:37AM +0800, Liu ping fan wrote:
> On Tue, Dec 13, 2011 at 7:36 PM, Marcelo Tosatti <mtosatti@redhat.com> wrote:
> > On Mon, Dec 12, 2011 at 10:41:23AM +0800, Liu Ping Fan wrote:
> >> From: Liu Ping Fan <pingfank@linux.vnet.ibm.com>
> >>
> >> Currently, vcpu can be destructed only when kvm instance destroyed.
> >> Change this to vcpu's destruction taken when its refcnt is zero,
> >> and then vcpu MUST and CAN be destroyed before kvm's destroy.
> >>
> >> Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com>
> >> ---
> >>  arch/x86/kvm/i8254.c     |   10 ++++--
> >>  arch/x86/kvm/i8259.c     |   12 +++++--
> >>  arch/x86/kvm/mmu.c       |    7 ++--
> >>  arch/x86/kvm/x86.c       |   54 +++++++++++++++++++----------------
> >>  include/linux/kvm_host.h |   71 ++++++++++++++++++++++++++++++++++++++++++----
> >>  virt/kvm/irq_comm.c      |    7 +++-
> >>  virt/kvm/kvm_main.c      |   62 +++++++++++++++++++++++++++++++++------
> >>  7 files changed, 170 insertions(+), 53 deletions(-)
> >
> > This needs a full audit of paths that access vcpus. See for one example
> > bsp_vcpu pointer.
> >
> Yes, I had missed it and just paid attention to the access path to
> vcpu in kvm_lapic and the path used in async_pf. I will correct it
> later.
> BTW, I want to make it sure that because kvm_lapic will be destroyed
> before vcpu, so  it is safe to bypass the access path there, and the
> situation is the same in async_pf for we have called
> kvm_clear_async_pf_completion_queue before zapping vcpu.  Am I right?
> 
> As to the scene like bsp_vcpu, I think that introducing refcount like
> in V2 can handle it easier. Please help to review these changes in V4
> which I will send a little later.
> 
Since bsp_vcpu pointer will never be released or re-assigned introducing
reference count to keep the pointer valid is not necessary. The counter
will never reach 0 and bsp vcpu will never be freed. Just disallow
removal of bsp_vcpu. Or better get rid of bsp_vcpu at all since its only
use is invalid anyway.

--
			Gleb.