Re: [PATCH v2 16/27] KVM: x86: Add a new page-track hook to handle memslot deletion

[Yan Zhao]

On Fri, Mar 10, 2023 at 04:22:47PM -0800, Sean Christopherson wrote:
> From: Yan Zhao <yan.y.zhao@xxxxxxxxx>
> 
> Add a new page-track hook, track_remove_region(), that is called when a
> memslot DELETE operation is about to be committed.  The "remove" hook
> will be used by KVMGT and will effectively replace the existing
> track_flush_slot() altogether now that KVM itself doesn't rely on the
> "flush" hook either.
> 
> The "flush" hook is flawed as it's invoked before the memslot operation
> is guaranteed to succeed, i.e. KVM might ultimately keep the existing
> memslot without notifying external page track users, a.k.a. KVMGT.  In
> practice, this can't currently happen on x86, but there are no guarantees
> that won't change in the future, not to mention that "flush" does a very
> poor job of describing what is happening.
> 
> Pass in the gfn+nr_pages instead of the slot itself so external users,
> i.e. KVMGT, don't need to exposed to KVM internals (memslots).  This will
> help set the stage for additional cleanups to the page-track APIs.
> 
> Cc: Zhenyu Wang <zhenyuw@xxxxxxxxxxxxxxx>
> Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
> Co-developed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
...

> +void kvm_page_track_delete_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_srcu(n, &head->track_notifier_list, node,
> +				srcu_read_lock_held(&head->track_srcu))
Sorry, not sure why the alignment here is not right.
Patchwork just sent me a mail to complain about it.
Would you mind helping fix it in the next version?

Thanks a lot!

> +		if (n->track_remove_region)
> +			n->track_remove_region(slot->base_gfn, slot->npages, n);
> +	srcu_read_unlock(&head->track_srcu, idx);
> +}
> +