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Date:   Fri, 16 Dec 2022 17:01:09 +0100
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Subject: Re: [PATCH 2/2] mm: Fix a few rare cases of using swapin error pte
 marker
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To:     Peter Xu <peterx@redhat.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Cc:     Andrea Arcangeli <aarcange@redhat.com>,
        Pengfei Xu <pengfei.xu@intel.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Huang Ying <ying.huang@intel.com>
References: <20221214200453.1772655-1-peterx@redhat.com>
 <20221214200453.1772655-3-peterx@redhat.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <20221214200453.1772655-3-peterx@redhat.com>
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> diff --git a/mm/memory.c b/mm/memory.c
> index 032ef700c3e8..3e836fecd035 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -828,7 +828,7 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
>   			return -EBUSY;
>   		return -ENOENT;
>   	} else if (is_pte_marker_entry(entry)) {
> -		if (userfaultfd_wp(dst_vma))
> +		if (is_swapin_error_entry(entry) || userfaultfd_wp(dst_vma))
>   			set_pte_at(dst_mm, addr, dst_pte, pte);

As discussed, it would be great if we could in the future avoid such 
allow lists and instead have default allow and only handle problematic 
cases. Maybe we can do that in the future with selective clearing of 
markers.

-- 
Thanks,

David / dhildenb