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Message-ID: <a60933f2-ef07-92a3-66cf-071670a03101@bytedance.com>
Date:   Sat, 7 May 2022 08:28:05 +0800
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Subject: Re: Re: [PATCH 3/4] mm/memofy-failure.c: optimize hwpoison_filter
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To:     David Hildenbrand <david@redhat.com>,
        Naoya Horiguchi <naoya.horiguchi@linux.dev>
Cc:     akpm@linux-foundation.org, naoya.horiguchi@nec.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Wu Fengguang <fengguang.wu@intel.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        "virtualization@lists.linux-foundation.org" 
        <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>
 <ac3fc5b9-d09c-5fb6-998d-f7c655d7fa00@redhat.com>
From:   zhenwei pi <pizhenwei@bytedance.com>
In-Reply-To: <ac3fc5b9-d09c-5fb6-998d-f7c655d7fa00@redhat.com>
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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).
>>
>> 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.
>>
>> 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).

>>
>> 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