Re: [PATCH 07/11] KVM: page track: add notifier support

[Xiao Guangrong]

On 12/16/2015 01:53 PM, Jike Song wrote:
> On 12/01/2015 02:26 AM, Xiao Guangrong wrote:
> > Notifier list is introduced so that any node wants to receive the track
> > event can register to the list
> >
> > Two APIs are introduced here:
> > - kvm_page_track_register_notifier(): register the notifier to receive
> >    track event
> >
> > - kvm_page_track_unregister_notifier(): stop receiving track event by
> >    unregister the notifier
> >
> > The callback, node->track_write() is called when a write access on the
> > write tracked page happens
> >
> > Signed-off-by: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx>
> > ---
> >   arch/x86/include/asm/kvm_host.h       |  1 +
> >   arch/x86/include/asm/kvm_page_track.h | 39 ++++++++++++++++++++
> >   arch/x86/kvm/page_track.c             | 67 +++++++++++++++++++++++++++++++++++
> >   arch/x86/kvm/x86.c                    |  4 +++
> >   4 files changed, 111 insertions(+)
> >
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index afff1f1..0f7b940 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -658,6 +658,7 @@ struct kvm_arch {
> >        */
> >       struct list_head active_mmu_pages;
> >       struct list_head zapped_obsolete_pages;
> > +    struct kvm_page_track_notifier_head track_notifier_head;
> >
> >       struct list_head assigned_dev_head;
> >       struct iommu_domain *iommu_domain;
> > diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h
> > index f223201..6744234 100644
> > --- a/arch/x86/include/asm/kvm_page_track.h
> > +++ b/arch/x86/include/asm/kvm_page_track.h
> > @@ -6,6 +6,36 @@ enum kvm_page_track_mode {
> >       KVM_PAGE_TRACK_MAX,
> >   };
> >
> > +/*
> > + * The notifier represented by @kvm_page_track_notifier_node is linked into
> > + * the head which will be notified when guest is triggering the track event.
> > + *
> > + * Write access on the head is protected by kvm->mmu_lock, read access
> > + * is protected by track_srcu.
> > + */
> > +struct kvm_page_track_notifier_head {
> > +    struct srcu_struct track_srcu;
> > +    struct hlist_head track_notifier_list;
> > +};
> > +
> > +struct kvm_page_track_notifier_node {
> > +    struct hlist_node node;
> > +
> > +    /*
> > +     * It is called when guest is writing the write-tracked page
> > +     * and write emulation is finished at that time.
> > +     *
> > +     * @vcpu: the vcpu where the write access happened.
> > +     * @gpa: the physical address written by guest.
> > +     * @new: the data was written to the address.
> > +     * @bytes: the written length.
> > +     */
> > +    void (*track_write)(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
> > +                int bytes);
>
> Sir, is it possible to make this non-void? as you described below, the
> callback may find this gpa isn't the page being tracked, so it probably
> want to return something to indicate: not my business, continue :)

Currently the return value is useless and it is not ABI so we can extend
it if it is needed in the future.

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