Re: [PATCH 1/2] KVM: page track: add a new notifier type: track_flush_slot

[Paolo Bonzini <pbonzini@redhat.com>]

On 10/10/2016 20:01, Neo Jia wrote:
>> Hi Neo,
>>
>> AFAIK this is needed because KVMGT doesn't paravirtualize the PPGTT,
>> while nVidia does.
> 
> Hi Paolo and Xiaoguang,
> 
> I am just wondering how device driver can register a notifier so he can be 
> notified for write-protected pages when writes are happening.

It can't yet, but the API is ready for that.  kvm_vfio_set_group is
currently where a struct kvm_device* and struct vfio_group* touch. Given
a struct kvm_device*, dev->kvm provides the struct kvm to be passed to
kvm_page_track_register_notifier.  So I guess you could add a callback
that passes the struct kvm_device* to the mdev device.

Xiaoguang and Guangrong, what were your plans?  We discussed it briefly
at KVM Forum but I don't remember the details.

Paolo

> Thanks,
> Neo
> 
>>
>> Paolo
>>
>>> Thanks,
>>> Neo
>>>
>>>>
>>>> Reviewed-by: Xiao Guangrong <guangrong.xiao@intel.com>
>>>> Signed-off-by: Chen Xiaoguang <xiaoguang.chen@intel.com>
>>>> ---
>>>>  arch/x86/include/asm/kvm_page_track.h |  9 +++++++++
>>>>  arch/x86/kvm/page_track.c             | 25 +++++++++++++++++++++++++
>>>>  arch/x86/kvm/x86.c                    |  2 +-
>>>>  3 files changed, 35 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h
>>>> index c2b8d24..5f66597 100644
>>>> --- a/arch/x86/include/asm/kvm_page_track.h
>>>> +++ b/arch/x86/include/asm/kvm_page_track.h
>>>> @@ -32,6 +32,14 @@ struct kvm_page_track_notifier_node {
>>>>  	 */
>>>>  	void (*track_write)(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
>>>>  			    int bytes);
>>>> +	/*
>>>> +	 * It is called when memory slot is being moved or removed
>>>> +	 * users can drop write-protection for the pages in that memory slot
>>>> +	 *
>>>> +	 * @kvm: the kvm where memory slot being moved or removed
>>>> +	 * @slot: the memory slot being moved or removed
>>>> +	 */
>>>> +	void (*track_flush_slot)(struct kvm *kvm, struct kvm_memory_slot *slot);
>>>>  };
>>>>  
>>>>  void kvm_page_track_init(struct kvm *kvm);
>>>> @@ -58,4 +66,5 @@ kvm_page_track_unregister_notifier(struct kvm *kvm,
>>>>  				   struct kvm_page_track_notifier_node *n);
>>>>  void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
>>>>  			  int bytes);
>>>> +void kvm_page_track_flush_slot(struct kvm *kvm, struct kvm_memory_slot *slot);
>>>>  #endif
>>>> diff --git a/arch/x86/kvm/page_track.c b/arch/x86/kvm/page_track.c
>>>> index b431539..e79bb25 100644
>>>> --- a/arch/x86/kvm/page_track.c
>>>> +++ b/arch/x86/kvm/page_track.c
>>>> @@ -225,3 +225,28 @@ void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
>>>>  			n->track_write(vcpu, gpa, new, bytes);
>>>>  	srcu_read_unlock(&head->track_srcu, idx);
>>>>  }
>>>> +
>>>> +/*
>>>> + * Notify the node that memory slot is being removed or moved so that it can
>>>> + * drop write-protection for the pages in the memory slot.
>>>> + *
>>>> + * The node should figure out it has any write-protected pages in this slot
>>>> + * by itself.
>>>> + */
>>>> +void kvm_page_track_flush_slot(struct kvm *kvm, struct kvm_memory_slot *slot)
>>>> +{
>>>> +	struct kvm_page_track_notifier_head *head;
>>>> +	struct kvm_page_track_notifier_node *n;
>>>> +	int idx;
>>>> +
>>>> +	head = &kvm->arch.track_notifier_head;
>>>> +
>>>> +	if (hlist_empty(&head->track_notifier_list))
>>>> +		return;
>>>> +
>>>> +	idx = srcu_read_lock(&head->track_srcu);
>>>> +	hlist_for_each_entry_rcu(n, &head->track_notifier_list, node)
>>>> +		if (n->track_flush_slot)
>>>> +			n->track_flush_slot(kvm, slot);
>>>> +	srcu_read_unlock(&head->track_srcu, idx);
>>>> +}
>>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>>> index 87f5dbb..f8ae90c 100644
>>>> --- a/arch/x86/kvm/x86.c
>>>> +++ b/arch/x86/kvm/x86.c
>>>> @@ -8278,7 +8278,7 @@ void kvm_arch_flush_shadow_all(struct kvm *kvm)
>>>>  void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
>>>>  				   struct kvm_memory_slot *slot)
>>>>  {
>>>> -	kvm_mmu_invalidate_zap_all_pages(kvm);
>>>> +	kvm_page_track_flush_slot(kvm, slot);
>>>>  }
>>>>  
>>>>  static inline bool kvm_vcpu_has_events(struct kvm_vcpu *vcpu)
>>>> -- 
>>>> 1.9.1
>>>>
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