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Date: Thu, 23 May 2024 05:08:29 +0200
From: Oscar Salvador <osalvador@suse.de>
To: Peter Xu <peterx@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andy Lutomirski <luto@kernel.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@kernel.org>,
	Borislav Petkov <bp@alien8.de>,
	Christophe Leroy <christophe.leroy@csgroup.eu>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	David Hildenbrand <david@redhat.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Helge Deller <deller@gmx.de>,
	Ingo Molnar <mingo@redhat.com>,
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	John Hubbard <jhubbard@nvidia.com>,
	Liu Shixin <liushixin2@huawei.com>,
	"Matthew Wilcox (Oracle)" <willy@infradead.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Muchun Song <muchun.song@linux.dev>,
	"Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
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	Peter Zijlstra <peterz@infradead.org>,
	Suren Baghdasaryan <surenb@google.com>,
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	linux-mm@kvack.org, linux-parisc@vger.kernel.org,
	linuxppc-dev@lists.ozlabs.org, x86@kernel.org
Subject: Re: [PATCH v2 1/1] arch/fault: don't print logs for pte marker
 poison errors
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On Wed, May 22, 2024 at 05:46:09PM -0400, Peter Xu wrote:
> > Now, ProcessB still has the page mapped, so upon re-accessing it,
> > it will trigger a new MCE event. memory-failure code will see that this
> 
> The question is why accessing that hwpoison entry from ProcB triggers an
> MCE.  Logically that's a swap entry and it should generate a page fault
> rather than MCE.  Then in the pgfault hanlder we don't need that encoded
> pfn as we have vmf->address.

It would be a swap entry if we reach try_to_umap_one() without trouble.
Then we have the code that converts it:

 ...
 if (PageHWPoison(p))
         pteval = swp_entry_to_pte(make_hwpoison_entry(subpage));
	 set_{huge_}pte_at
 ...

But maybe we could only do that for ProcA, while ProcB failed to do that,
which means that for ProcA that is a hwpoisoned-swap-entry, but ProcB still
has this page mapped as usual, so if ProcB re-access it, that will not
trigger a fault (because the page is still mapped in its pagetables).


-- 
Oscar Salvador
SUSE Labs