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Tsirkin" , Jason Wang , "virtualization@lists.linux-foundation.org" References: <20220429142206.294714-1-pizhenwei@bytedance.com> <20220429142206.294714-4-pizhenwei@bytedance.com> <20220506085920.GC1356094@u2004> <3c0e25fb-695d-4a29-6de4-c892f89cea7a@bytedance.com> <20220507082045.GA1716199@u2004> From: zhenwei pi In-Reply-To: <20220507082045.GA1716199@u2004> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/7/22 16:20, Naoya Horiguchi wrote: > 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. > OK, I'll remove this patch(mm/memofy-failure.c: optimize hwpoison_filter) from this series, and fix the other 3 patches in the v2 version. Then try to implement/test as your suggestion in another series. >>>> >>>> 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 > Yes, it's my plan. Thanks for your suggestions! >> >>>> >>>> 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 -- zhenwei pi