On Thu, Aug 29, 2013 at 05:31:42PM +0800, Xiao Guangrong wrote: > > As Documentation/RCU/whatisRCU.txt says: > > > > As with rcu_assign_pointer(), an important function of > > rcu_dereference() is to document which pointers are protected by > > RCU, in particular, flagging a pointer that is subject to changing > > at any time, including immediately after the rcu_dereference(). > > And, again like rcu_assign_pointer(), rcu_dereference() is > > typically used indirectly, via the _rcu list-manipulation > > primitives, such as list_for_each_entry_rcu(). > > > > The documentation aspect of rcu_assign_pointer()/rcu_dereference() is > > important. The code is complicated, so self documentation will not hurt. > > I want to see what is actually protected by rcu here. Freeing shadow > > pages with call_rcu() further complicates matters: does it mean that > > shadow pages are also protected by rcu? > > Yes, it stops shadow page to be freed when we do write-protection on > it. > Yeah, I got the trick, what I am saying that we have a data structure here protected by RCU, but we do not use RCU functions to access it... BTW why not allocate sp->spt from SLAB_DESTROY_BY_RCU cache too? We may switch write protection on a random spt occasionally if page is deleted and reused for another spt though. For last level spt it should not be a problem and for non last level we have is_last_spte() check in __rmap_write_protect_lockless(). Can it work? -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
