Re: [PATCH] mm,hwpoison: return -EBUSY when page already poisoned

[Aili Yao]

On Thu, 4 Mar 2021 10:16:53 +0800
Aili Yao <yaoaili@xxxxxxxxxxxx> wrote:

> On Wed, 3 Mar 2021 15:41:35 +0000
> "Luck, Tony" <tony.luck@xxxxxxxxx> wrote:
> 
> > > For error address with sigbus, i think this is not an issue resulted by the patch i post, before my patch, the issue is already there.
> > > I don't find a realizable way to get the correct address for same reason --- we don't know whether the page mapping is there or not when
> > > we got to kill_me_maybe(), in some case, we may get it, but there are a lot of parallel issue need to consider, and if failed we have to fallback
> > > to the error brach again, remaining current code may be an easy option;    
> > 
> > My RFC patch from yesterday removes the uncertainty about whether the page is there or not. After it walks the page
> > tables we know that the poison page isn't mapped (note that patch is RFC for a reason ... I'm 90% sure that it should
> > do a bit more that just clear the PRESENT bit).
> > 
> > So perhaps memory_failure() has queued a SIGBUS for this task, if so, we take it when we return from kill_me_maybe()

And when this happen, the process will receive an SIGBUS with AO level, is it proper as not an AR?

> > If not, we will return to user mode and re-execute the failing instruction ... but because the page is unmapped we will take a #PF  
> 
> Got this, I have some error thoughts here.
> 
> 
> > The x86 page fault handler will see that the page for this physical address is marked HWPOISON, and it will send the SIGBUS
> > (just like it does if the page had been removed by an earlier UCNA/SRAO error).  
> 
> if your methods works, should it be like this?
> 
> 1582                         pteval = swp_entry_to_pte(make_hwpoison_entry(subpage));
> 1583                         if (PageHuge(page)) {
> 1584                                 hugetlb_count_sub(compound_nr(page), mm);
> 1585                                 set_huge_swap_pte_at(mm, address,
> 1586                                                      pvmw.pte, pteval,
> 1587                                                      vma_mmu_pagesize(vma));
> 1588                         } else {
> 1589                                 dec_mm_counter(mm, mm_counter(page));
> 1590                                 set_pte_at(mm, address, pvmw.pte, pteval);
> 1591                         }
> 
> the page fault check if it's a poison page using is_hwpoison_entry(),
> 

And if it works, does we need some locking mechanism before we call walk_page_range();
if we lock, does we need to process the blocking interrupted error as other places will do?

-- 
Thanks!
Aili Yao