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

["HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>]

On Tue, Jun 07, 2022 at 02:59:59PM -0700, Andrew Morton wrote:
> On Tue, 7 Jun 2022 14:36:00 +0200 David Hildenbrand <david@redhat.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, the impact of the bug is limited.

> 
> 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?

mf_mutex is to ensure that only one error handling thread can handle
the pfn at one time, but set_mce_nospec() is called outside it now.
So if we want to prevent the race with unmap, both of set_mce_nospec()
and the new kpte check might need to be done in mf_mutex.

- Naoya Horiguchi