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Date: Mon, 3 Sep 2018 16:33:12 -0700
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 1/1] userfaultfd: allow
 get_mempolicy(MPOL_F_NODE|MPOL_F_ADDR) to trigger userfaults
Message-Id: <20180903163312.4d758536e1208f8927d886e9@linux-foundation.org>
In-Reply-To: <20180831214848.23676-1-aarcange@redhat.com>
References: <20180831214848.23676-1-aarcange@redhat.com>
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To: Andrea Arcangeli <aarcange@redhat.com>
Cc: linux-mm@kvack.org, Maxime Coquelin <maxime.coquelin@redhat.com>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, Mike Rapoport <rppt@linux.vnet.ibm.com>

On Fri, 31 Aug 2018 17:48:48 -0400 Andrea Arcangeli <aarcange@redhat.com> wrote:

> get_mempolicy(MPOL_F_NODE|MPOL_F_ADDR) called a get_user_pages that
> would not be waiting for userfaults before failing and it would hit on
> a SIGBUS instead. Using get_user_pages_locked/unlocked instead will
> allow get_mempolicy to allow userfaults to resolve the fault and fill
> the hole, before grabbing the node id of the page.

What is the userspace visible impact of this change?