linux-kernel - Re: [PATCH] mm/memory-failure: don't allow to unpoison hw corrupted page

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Date:   Wed, 8 Jun 2022 11:45:24 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     HORIGUCHI NAOYA (堀口 直也) 
        <naoya.horiguchi@....com>, zhenwei pi <pizhenwei@...edance.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Tony Luck <tony.luck@...el.com>,
        Wu Fengguang <fengguang.wu@...el.com>
Subject: Re: [PATCH] mm/memory-failure: don't allow to unpoison hw corrupted
 page

On 07.06.22 23:59, Andrew Morton wrote:
> On Tue, 7 Jun 2022 14:36:00 +0200 David Hildenbrand <david@...hat.com> wrote:
> 
>> On 06.06.22 11:15, HORIGUCHI NAOYA(堀口 直也) wrote:
>>>>>    [  917.864266]  <TASK>
>>>>>    [  917.864961]  clear_huge_page+0x147/0x270
>>>>>    [  917.866236]  hugetlb_fault+0x440/0xad0
>>>>>    [  917.867366]  handle_mm_fault+0x270/0x290
>>>>>    [  917.868532]  do_user_addr_fault+0x1c3/0x680
>>>>>    [  917.869768]  exc_page_fault+0x6c/0x160
>>>>>    [  917.870912]  ? asm_exc_page_fault+0x8/0x30
>>>>>    [  917.872082]  asm_exc_page_fault+0x1e/0x30
>>>>>    [  917.873220] RIP: 0033:0x7f2aeb8ba367
>>>>>
>>>>> I don't think of a workaround for this now ...
>>>>>
>>>>
>>>> Could you please tell me how to reproduce this issue?
>>>
>>> You are familiar with qemu-monitor-command, so the following procedure
>>> should work for you:
>>>
>>>   - run a process using hugepages on your VM,
>>>   - check the guest physical address of the hugepage (page-types.c is helpful for this),
>>>   - inject a MCE with virsh qemu-monitor-command on the guest physical address, then
>>>   - unpoison the injected physical address.
>>
>> That's triggered via debugfs / HWPOISON_INJECT, right?
>>
>> That's a DEBUG_KERNEL option, so I'm not 100% sure if we really want to
>> cc stable.
> 
> Sure, it's hardly a must-have.  But let's also take the patch
> complexity&risk into account.  This is one dang simple patch.
> 
> Or is it.  Should these things be happening outside mf_mutex?  What the
> heck is the role of mf_mutex anyway?

For example, I'm not even sure if we're allowed to use virt_to_kpte()
out of random context at all.

If we have a PMD direct map, why should it be okay to use virt_to_kpte()?

Maybe I am just wrong, I asked that question on the next patch version
as well.

-- 
Thanks,

David / dhildenb