On 30/11/2015 19:26, Xiao Guangrong wrote: > This patchset introduces the feature which allows us to track page > access in guest. Currently, only write access tracking is implemented > in this version. > > Four APIs are introduces: > - kvm_page_track_add_page(kvm, gfn, mode), single guest page @gfn is > added into the track pool of the guest instance represented by @kvm, > @mode specifies which kind of access on the @gfn is tracked > > - kvm_page_track_remove_page(kvm, gfn, mode), is the opposed operation > of kvm_page_track_add_page() which removes @gfn from the tracking pool. > gfn is no tracked after its last user is gone > > - kvm_page_track_register_notifier(kvm, n), register a notifier so that > the event triggered by page tracking will be received, at that time, > the callback of n->track_write() will be called > > - kvm_page_track_unregister_notifier(kvm, n), does the opposed operation > of kvm_page_track_register_notifier(), which unlinks the notifier and > stops receiving the tracked event > > The first user of page track is non-leaf shadow page tables as they are > always write protected. It also gains performance improvement because > page track speeds up page fault handler for the tracked pages. The > performance result of kernel building is as followings: > > before after > real 461.63 real 455.48 > user 4529.55 user 4557.88 > sys 1995.39 sys 1922.57 For KVM-GT, as far as I know Andrea Arcangeli is working on extending userfaultfd to tracking write faults only. Perhaps KVM-GT can do something similar, where KVM gets the write tracking functionality for free through the MMU notifiers. Any thoughts on this? Applying your technique to non-leaf shadow pages actually makes this series quite interesting. :) Shadow paging is still in use for nested EPT, so it's always a good idea to speed it up. Paolo -- 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
