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[14.202.194.140]) by smtp.gmail.com with ESMTPSA id s14-v6sm20244808pfj.105.2018.08.31.02.27.27 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 31 Aug 2018 02:27:28 -0700 (PDT) Date: Fri, 31 Aug 2018 19:27:24 +1000 From: Balbir Singh To: jglisse@redhat.com Cc: linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org, Ralph Campbell , "Kirill A . Shutemov" , stable@vger.kernel.org Subject: Re: [PATCH 3/7] mm/rmap: map_pte() was not handling private ZONE_DEVICE page properly v2 Message-ID: <20180831092724.GD28695@350D> References: <20180824192549.30844-3-jglisse@redhat.com> <20180830144156.7226-1-jglisse@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20180830144156.7226-1-jglisse@redhat.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 30, 2018 at 10:41:56AM -0400, jglisse@redhat.com wrote: > From: Ralph Campbell > > Private ZONE_DEVICE pages use a special pte entry and thus are not > present. Properly handle this case in map_pte(), it is already handled > in check_pte(), the map_pte() part was lost in some rebase most probably. > > Without this patch the slow migration path can not migrate back private > ZONE_DEVICE memory to regular memory. This was found after stress > testing migration back to system memory. This ultimatly can lead the > CPU to an infinite page fault loop on the special swap entry. > > Changes since v1: > - properly lock pte directory in map_pte() > > Signed-off-by: Ralph Campbell > Signed-off-by: Jérôme Glisse > Cc: Andrew Morton > Cc: Kirill A. Shutemov > Cc: Balbir Singh > Cc: stable@vger.kernel.org > --- > mm/page_vma_mapped.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c > index ae3c2a35d61b..bd67e23dce33 100644 > --- a/mm/page_vma_mapped.c > +++ b/mm/page_vma_mapped.c > @@ -21,7 +21,14 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw) > if (!is_swap_pte(*pvmw->pte)) > return false; > } else { > - if (!pte_present(*pvmw->pte)) > + if (is_swap_pte(*pvmw->pte)) { > + swp_entry_t entry; > + > + /* Handle un-addressable ZONE_DEVICE memory */ > + entry = pte_to_swp_entry(*pvmw->pte); > + if (!is_device_private_entry(entry)) > + return false; OK, so we skip this pte from unmap since it's already unmapped? This prevents try_to_unmap from unmapping it and it gets restored with MIGRATE_PFN_MIGRATE flag cleared? Sounds like the right thing, if I understand it correctly Acked-by: Balbir Singh Balbir Singh.