Re: [test result] dirty logging without srcu update -- Re: [RFC][PATCH] srcu: Implement call_srcu()

[Takuya Yoshikawa <takuya.yoshikawa@gmail.com>]

Avi Kivity <avi@redhat.com> wrote:

> > I have one concern about correctness issue though:
> >
> >     concurrent rmap write protection may not be safe due to
> >     delayed tlb flush ... cannot happen?
> 
> What do you mean by concurrent rmap write protection?
> 

Not sure, but other codes like:

- mmu_sync_children()
	for_each_sp(pages, sp, parents, i)
		protected |= rmap_write_protect(vcpu->kvm, sp->gfn);

		if (protected)
			kvm_flush_remote_tlbs(vcpu->kvm);

- kvm_mmu_get_page()
	if (rmap_write_protect(vcpu->kvm, gfn))
		kvm_flush_remote_tlbs(vcpu->kvm);

I just wondered what can happen if GET_DIRTY_LOG is being processed
behind these processing?

They may find nothing to write protect and won't do kvm_flush_remote_tlbs()
if the gfn has been already protected by GET_DIRTY_LOG.

But GET_DIRTY_LOG may still be busy write protecting other pages and
others can return before.  (My code releases mmu_lock to not include
__put_user() in the critical section.)

I am not still enough familier with these code yet.
(maybe empty concern)

	Takuya