linux-kernel - Re: [PATCH v2 1/1] arch/fault: don't print logs for pte marker poison errors

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Date: Thu, 23 May 2024 05:08:29 +0200
From: Oscar Salvador <osalvador@...e.de>
To: Peter Xu <peterx@...hat.com>
Cc: Axel Rasmussen <axelrasmussen@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	David Hildenbrand <david@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Helge Deller <deller@....de>,
	Ingo Molnar <mingo@...hat.com>,
	"James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
	John Hubbard <jhubbard@...dia.com>,
	Liu Shixin <liushixin2@...wei.com>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Muchun Song <muchun.song@...ux.dev>,
	"Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
	Nicholas Piggin <npiggin@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-parisc@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: Re: [PATCH v2 1/1] arch/fault: don't print logs for pte marker
 poison errors

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