Re: [PATCH 3/3] add support for change_pte mmu notifiers

[Andrea Arcangeli <aarcange@redhat.com>]

On Wed, Sep 23, 2009 at 09:47:18PM +0300, Izik Eidus wrote:
> +	if (need_flush)
> +		kvm_flush_remote_tlbs(kvm);

need_flush can be return to kvm_mmu_notifier_change_pte to defer the
tlb flush after dropping the spin lock I think. We are forced to flush
the tlb inside spin_lock in kvm normal context because that stops the
VM from freeing the page (it hangs on the mmu_lock taken by kvm
invalidate_page/change_pte) so we can unmap tons of sptes and do a
single kvm tlb flush that covers them all (by keeping both actions
under the mmu_lock), but in mmu notifier context the pages can't be
freed from under the guest, so we can flush the tlb flushing the tlb
before making the page freeable, because both old and new page in
do_wp_page are still pinned and can't be freed and reused from under
us even if we release mmu_lock before tlb flush.