Re: [PATCH v5] mm/gup: check page hwposion status for coredump.

[David Hildenbrand]

On 26.03.21 15:09, David Hildenbrand wrote:
> On 22.03.21 12:33, Aili Yao wrote:
> > When we do coredump for user process signal, this may be one SIGBUS signal
> > with BUS_MCEERR_AR or BUS_MCEERR_AO code, which means this signal is
> > resulted from ECC memory fail like SRAR or SRAO, we expect the memory
> > recovery work is finished correctly, then the get_dump_page() will not
> > return the error page as its process pte is set invalid by
> > memory_failure().
> >
> > But memory_failure() may fail, and the process's related pte may not be
> > correctly set invalid, for current code, we will return the poison page,
> > get it dumped, and then lead to system panic as its in kernel code.
> >
> > So check the hwpoison status in get_dump_page(), and if TRUE, return NULL.
> >
> > There maybe other scenario that is also better to check hwposion status
> > and not to panic, so make a wrapper for this check, Thanks to David's
> > suggestion(<david@xxxxxxxxxx>).
> >
> > Link: https://lkml.kernel.org/r/20210319104437.6f30e80d@alex-virtual-machine
> > Signed-off-by: Aili Yao <yaoaili@xxxxxxxxxxxx>
> > Cc: David Hildenbrand <david@xxxxxxxxxx>
> > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> > Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
> > Cc: Oscar Salvador <osalvador@xxxxxxx>
> > Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> > Cc: Aili Yao <yaoaili@xxxxxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > ---
> >    mm/gup.c      |  4 ++++
> >    mm/internal.h | 20 ++++++++++++++++++++
> >    2 files changed, 24 insertions(+)
> >
> > diff --git a/mm/gup.c b/mm/gup.c
> > index e4c224c..6f7e1aa 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -1536,6 +1536,10 @@ struct page *get_dump_page(unsigned long addr)
> >    				      FOLL_FORCE | FOLL_DUMP | FOLL_GET);
> >    	if (locked)
> >    		mmap_read_unlock(mm);
>
> Thinking again, wouldn't we get -EFAULT from __get_user_pages_locked()
> when stumbling over a hwpoisoned page?
>
> See __get_user_pages_locked()->__get_user_pages()->faultin_page():
>
> handle_mm_fault()->vm_fault_to_errno(), which translates
> VM_FAULT_HWPOISON to -EFAULT, unless FOLL_HWPOISON is set (-> -EHWPOISON)
>
> ?

Or doesn't that happen as you describe "But memory_failure() may fail, 
and the process's related pte may not be correctly set invalid" -- but 
why does that happen?

On a similar thought, should get_user_pages() never return a page that 
has HWPoison set? E.g., check also for existing PTEs if the page is 
hwpoisoned?

@Naoya, Oscar

--
Thanks,

David / dhildenb