Hi, On 10/01/2014 18:57, Andrea Arcangeli wrote: > Hi! > > On Fri, Jan 10, 2014 at 06:38:06PM +0200, Izik Eidus wrote: >> It look like commit 6bdb913f0a70a4dfb7f066fb15e2d6f960701d00 break the >> semantic of set_pte_at_notify. >> The change of calling first to mmu_notifier_invalidate_range_start, then >> to set_pte_at_notify, and then to mmu_notifier_invalidate_range_end >> not only increase the amount of locks kvm have to take and release by >> factor of 3, but in addition mmu_notifier_invalidate_range_start is zapping >> the pte entry from kvm, so when set_pte_at_notify get called, it doesn`t >> have any spte to set and it acctuly get called for nothing, the result is >> increasing of vmexits for kvm from both do_wp_page and replace_page, and >> broken semantic of set_pte_at_notify. > > Agreed. > > I would suggest to change set_pte_at_notify to return if change_pte > was missing in some mmu notifier attached to this mm, so we can do > something like: > > ptep = page_check_address(page, mm, addr, &ptl, 0); > [..] > notify_missing = false; > if (... ) { > entry = ptep_clear_flush(...); > [..] > notify_missing = set_pte_at_notify(mm, addr, ptep, entry); > } > pte_unmap_unlock(ptep, ptl); > if (notify_missing) > mmu_notifier_invalidate_page_if_missing_change_pte(mm, addr); > > and drop the range calls. This will provide sleepability and at the > same time it won't screw the ability of change_pte to update sptes (by > leaving those established by the time change_pte runs). I think it would be better for notifiers that do not support change_pte to keep getting both range_start and range_end notifiers. Otherwise, the invalidate_page notifier might end up marking the old page as dirty after it was already replaced in the primary page table. Perhaps we can have a flag in the mmu_notifier, similar to the notify_missing returned value here, that determines in these cases whether to call the invalidate_range_start/end pair, or just the set_pte_at_notify. Thanks, Haggai -- 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