From mboxrd@z Thu Jan  1 00:00:00 1970
From: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
Subject: Re: [PATCH 1/2] KVM: page track: add a new notifier type:
 track_flush_slot
Date: Wed, 12 Oct 2016 22:48:27 +0200
Message-ID: <20161012204827.GA15270@potion>
References: <1475998904-13456-1-git-send-email-xiaoguang.chen@intel.com>
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Cc: kvm@vger.kernel.org, pbonzini@redhat.com, guangrong.xiao@intel.com,
        jike.song@intel.com
To: Xiaoguang Chen <xiaoguang.chen@intel.com>
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2016-10-09 15:41+0800, Xiaoguang Chen:
> When a memory slot is being moved or removed users of page track
> can be notified. So users can drop write-protection for the pages
> in that memory slot.
> 
> This notifier type is needed by KVMGT to sync up its shadow page
> table when memory slot is being moved or removed.
> 
> Reviewed-by: Xiao Guangrong <guangrong.xiao@intel.com>
> Signed-off-by: Chen Xiaoguang <xiaoguang.chen@intel.com>
> ---
> diff --git 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,
> +
> +/*
> + * 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);
> +}

We repeat the same drill for the other page_track_notifier as well ...
I was thinking it would be nice to have something like:

  void kvm_page_track_flush_slot(struct kvm *kvm, struct kvm_memory_slot *slot)
  {
  	struct kvm_page_track_notifier_node *n;
  	int i;

  	kvm_for_each_track_notifier(n, &kvm->arch.track_notifier_head, i)
  		if (n->track_flush_slot)
  			n->track_flush_slot(kvm, slot);
  }

which requires this monster:

  #define kvm_for_each_track_notifier(notifier, head, tmp) \
  	for (tmp = !hlist_empty(&(head)->track_notifier_list); \
  	     tmp && ({tmp = srcu_read_lock(&(head)->track_srcu); true;}); \
  	     srcu_read_unlock(&(head)->track_srcu, tmp), tmp = 0) \
  		hlist_for_each_entry_rcu(notifier, &(head)->track_notifier_list, node)

so waiting for more notifiers doesn't seem that bad. :)