linux-kernel - Re: [PATCH v1] mm, pagemap: expose hwpoison entry

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Date:   Wed, 13 Oct 2021 10:49:04 +0800
From:   Peter Xu <peterx@...hat.com>
To:     Naoya Horiguchi <naoya.horiguchi@...ux.dev>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Alistair Popple <apopple@...dia.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Konstantin Khlebnikov <koct9i@...il.com>,
        Bin Wang <wangbin224@...wei.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] mm, pagemap: expose hwpoison entry

Hi, Naoya,

On Mon, Oct 04, 2021 at 08:50:01PM +0900, Naoya Horiguchi wrote:
> +static inline struct page *hwpoison_entry_to_page(swp_entry_t entry)
> +{
> +	struct page *p = pfn_to_page(swp_offset(entry));
> +
> +	WARN_ON(!PageHWPoison(p));
> +	return p;
> +}

This is more a pure question..

I'm wondering whether that WARN_ON() could trigger.

IOW, what if we poison an anonymous page and then unpoison it?  Will there be a
hwpoison swap entry leftover in the ptes that it used to map?  Will it crash
the program when the page is accessed?

I had a feeling that when handling the page fault in do_swap_page before we
SIGBUS the program, we should double-check the PageHWPoison on the pfn page,
but I could be missing something..

Thanks,

-- 
Peter Xu