Re: [PATCH v7 06/14] KVM: Make dirty ring exclusive to dirty bitmap log

Peter Xu
2020-03-23T16:16:35Z

On Sat, Mar 21, 2020 at 12:12:50PM -0700, Sean Christopherson wrote:
> On Wed, Mar 18, 2020 at 12:37:12PM -0400, Peter Xu wrote:
> > There's no good reason to use both the dirty bitmap logging and the
> > new dirty ring buffer to track dirty bits. We should be able to even
> > support both of them at the same time, but it could complicate things
> > which could actually help little. Let's simply make it the rule
> > before we enable dirty ring on any arch, that we don't allow these two
> > interfaces to be used together.
> >
> > The big world switch would be KVM_CAP_DIRTY_LOG_RING capability
> > enablement. That's where we'll switch from the default dirty logging
> > way to the dirty ring way. As long as kvm->dirty_ring_size is setup
> > correctly, we'll once and for all switch to the dirty ring buffer mode
> > for the current virtual machine.
> >
> > Signed-off-by: Peter Xu <peterx@redhat.com>
> > ---
> > Documentation/virt/kvm/api.rst | 7 +++++++
> > virt/kvm/kvm_main.c | 12 ++++++++++++
> > 2 files changed, 19 insertions(+)
> >
> > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> > index 99ee9cfc20c4..8f3a83298d3f 100644
> > --- a/Documentation/virt/kvm/api.rst
> > +++ b/Documentation/virt/kvm/api.rst
> > @@ -6202,3 +6202,10 @@ make sure all the existing dirty gfns are flushed to the dirty rings.
> >
> > The dirty ring can gets full. When it happens, the KVM_RUN of the
> > vcpu will return with exit reason KVM_EXIT_DIRTY_LOG_FULL.
> > +
> > +NOTE: the KVM_CAP_DIRTY_LOG_RING capability and the new ioctl
>
> Leave off "new", it'll be stale a few months/years from now.

Ok.

>
> > +KVM_RESET_DIRTY_RINGS are exclusive to the existing KVM_GET_DIRTY_LOG
>
> Did you mean "mutually exclusive with"? "exclusive to" would mean they
> can only be used by KVM_GET_DIRTY_LOG with doesn't match the next
> sentence.

I meant "mutual-exclusive". I'll fix it up.

Thanks,

--
Peter Xu