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Date:   Mon, 30 May 2022 13:46:57 +0800
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Subject: Re: Re: [PATCH 2/3] mm/memory-failure.c: support reset PTE during
 unpoison
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 <20220530050234.GA1036127@hori.linux.bs1.fc.nec.co.jp>
From:   zhenwei pi <pizhenwei@bytedance.com>
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On 5/30/22 13:02, HORIGUCHI NAOYA(堀口 直也) wrote:
> On Fri, May 20, 2022 at 03:06:47PM +0800, zhenwei pi wrote:
>> Origianlly, unpoison_memory() is only used by hwpoison-inject, and
>> unpoisons a page which is poisoned by hwpoison-inject too. The kernel PTE
>> entry has no change during software poison/unpoison.
>>
>> On a virtualization platform, it's possible to fix hardware corrupted page
>> by hypervisor, typically the hypervisor remaps the error HVA(host virtual
>> address). So add a new parameter 'const char *reason' to show the reason
>> called by.
>>
>> Once the corrupted page gets fixed, the guest kernel needs put page to
>> buddy. Reuse the page and hit the following issue(Intel Platinum 8260):
>>   BUG: unable to handle page fault for address: ffff888061646000
>>   #PF: supervisor write access in kernel mode
>>   #PF: error_code(0x0002) - not-present page
>>   PGD 2c01067 P4D 2c01067 PUD 61aaa063 PMD 10089b063 PTE 800fffff9e9b9062
>>   Oops: 0002 [#1] PREEMPT SMP NOPTI
>>   CPU: 2 PID: 31106 Comm: stress Kdump: loaded Tainted: G   M       OE     5.18.0-rc6.bm.1-amd64 #6
>>   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
>>   RIP: 0010:clear_page_erms+0x7/0x10
>>
>> The kernel PTE entry of the fixed page is still uncorrected, kernel hits
>> page fault during prep_new_page. So add 'bool reset_kpte' to get a change
>> to fix the PTE entry if the page is fixed by hypervisor.
>>
>> Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
>> ---
>>   include/linux/mm.h   |  2 +-
>>   mm/hwpoison-inject.c |  2 +-
>>   mm/memory-failure.c  | 26 +++++++++++++++++++-------
>>   3 files changed, 21 insertions(+), 9 deletions(-)
>>
> 
> Do you need undoing rate limiting here?  In the original unpoison's usage,
> avoiding flood of "Unpoison: Software-unpoisoned page" messages is helpful.
> 
> And unpoison seems to be called from virtio-balloon multiple times when
> the backend is 2MB hugepages.  If it's right, printing out 512 lines of
> "Unpoison: Unpoisoned page 0xXXX by virtio-balloon" messages might not be
> so helpful?
> 

All the suggestions(include '[PATCH 1/3] memory-failure: Introduce 
memory failure notifier') are reasonable, I'll fix them in the next 
version. Thanks a lot!


-- 
zhenwei pi