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

From: Takuya Yoshikawa
Date: Thu Feb 02 2012 - 09:44:55 EST

Avi Kivity <avi@xxxxxxxxxx> 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_mmu_get_page()
if (rmap_write_protect(vcpu->kvm, gfn))

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)

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