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

[Xiao Guangrong <guangrong.xiao@linux.intel.com>]

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@linux.intel.com>
>> ---
>>   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.