On Sat, May 07, 2022 at 08:28:05AM +0800, zhenwei pi wrote: > > On 5/7/22 00:28, David Hildenbrand wrote: > > On 06.05.22 15:38, zhenwei pi wrote: > > > > > > > > > On 5/6/22 16:59, Naoya Horiguchi wrote: > > > > On Fri, Apr 29, 2022 at 10:22:05PM +0800, zhenwei pi wrote: > > > > > In the memory failure procedure, hwpoison_filter has higher priority, > > > > > if memory_filter() filters the error event, there is no need to do > > > > > the further work. > > > > > > > > Could you clarify what problem you are trying to solve (what does > > > > "optimize" mean in this context or what is the benefit)? > > > > > > > > > > OK. The background of this work: > > > As well known, the memory failure mechanism handles memory corrupted > > > event, and try to send SIGBUS to the user process which uses this > > > corrupted page. > > > > > > For the virtualization case, QEMU catches SIGBUS and tries to inject MCE > > > into the guest, and the guest handles memory failure again. Thus the > > > guest gets the minimal effect from hardware memory corruption. > > > > > > The further step I'm working on: > > > 1, try to modify code to decrease poisoned pages in a single place > > > (mm/memofy-failure.c: simplify num_poisoned_pages_dec in this series). This is fine to me. > > > > > > 2, try to use page_handle_poison() to handle SetPageHWPoison() and > > > num_poisoned_pages_inc() together. It would be best to call > > > num_poisoned_pages_inc() in a single place too. I'm not sure if this is > > > possible or not, please correct me if I misunderstand. SetPageHWPoison() can be cancelled in memory_failure(), so simply bundling it with num_poisoned_pages_inc() might not be optimal. I think that action_result() is supposed to be called when memory error handling is effective (not filtered, not cancelled). So moving num_poisoned_pages_inc() (and notification code in your plan) into this function might be good. > > > > > > 3, introduce memory failure notifier list in memory-failure.c: notify > > > the corrupted PFN to someone who registers this list. > > > If I can complete [1] and [2] part, [3] will be quite easy(just call > > > notifier list after increasing poisoned page). > > > > > > 4, introduce memory recover VQ for memory balloon device, and registers > > > memory failure notifier list. During the guest kernel handles memory > > > failure, balloon device gets notified by memory failure notifier list, > > > and tells the host to recover the corrupted PFN(GPA) by the new VQ. > > > > Most probably you might want to do that asynchronously, and once the > > callback succeeds, un-poison the page. > > > Yes! > > > > > > > 5, host side remaps the corrupted page(HVA), and tells the guest side to > > > unpoison the PFN(GPA). Then the guest fixes the corrupted page(GPA) > > > dynamically. > > > > I think QEMU already does that during reboots. Now it would be triggered > > by the guest for individual pages. > > > Yes, currently QEMU supports to un-poison corrupted pages during > reset/reboot. We can reuse some code to do the work in this case, this > allows a VM to fix corrupted pages as soon as possible(also no need to > reset/reboot). So this finally allows to replace broken page mapped to guest with a healthy page without rebooting the guest. That sounds helpful. Thanks, Naoya Horiguchi > > > > > > > Because [4] and [5] are related to balloon device, also CC Michael, > > > David and Jason. > > > > Doesn't sound too crazy for me, although it's a shame that we always > > have to use virtio-balloon for such fairly balloon-unrelated things. > > > Thanks! > > -- > zhenwei pi
