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Wed, 11 Nov 2020 04:25:32 -0500 X-MC-Unique: FDXqpnHGNXqJDzJFikjeLA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C89DF188C127; Wed, 11 Nov 2020 09:25:29 +0000 (UTC) Received: from [10.36.114.151] (ovpn-114-151.ams2.redhat.com [10.36.114.151]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7DF15413C; Wed, 11 Nov 2020 09:25:27 +0000 (UTC) Subject: Re: [PATCH v1] mm/page_alloc: clear pages in alloc_contig_pages() with init_on_alloc=1 or __GFP_ZERO To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Andrew Morton , Alexander Potapenko , Michal Hocko , Mike Kravetz , Vlastimil Babka , Mike Rapoport , Oscar Salvador , Kees Cook , Michael Ellerman References: <20201110193240.25401-1-david@redhat.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <75483ee9-f030-74ac-4b4f-732fb512280b@redhat.com> Date: Wed, 11 Nov 2020 10:25:26 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20201110193240.25401-1-david@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 10.11.20 20:32, David Hildenbrand wrote: > commit 6471384af2a6 ("mm: security: introduce init_on_alloc=1 and > init_on_free=1 boot options") resulted with init_on_alloc=1 in all pages > leaving the buddy via alloc_pages() and friends to be > initialized/cleared/zeroed on allocation. > > However, the same logic is currently not applied to > alloc_contig_pages(): allocated pages leaving the buddy aren't cleared > with init_on_alloc=1 and init_on_free=0. Let's also properly clear > pages on that allocation path and add support for __GFP_ZERO. > > With this change, we will see double clearing of pages in some > cases. One example are gigantic pages (either allocated via CMA, or > allocated dynamically via alloc_contig_pages()) - which is the right > thing to do (and to be optimized outside of the buddy in the callers) as > discussed in: > https://lkml.kernel.org/r/20201019182853.7467-1-gpiccoli@canonical.com > > This change implies that with init_on_alloc=1 > - All CMA allocations will be cleared > - Gigantic pages allocated via alloc_contig_pages() will be cleared > - virtio-mem memory to be unplugged will be cleared. While this is > suboptimal, it's similar to memory balloon drivers handling, where > all pages to be inflated will get cleared as well. > > Cc: Andrew Morton > Cc: Alexander Potapenko > Cc: Michal Hocko > Cc: Mike Kravetz > Cc: Vlastimil Babka > Cc: Mike Rapoport > Cc: Oscar Salvador > Cc: Kees Cook > Cc: Michael Ellerman > Signed-off-by: David Hildenbrand > --- > mm/page_alloc.c | 24 +++++++++++++++++++++--- > 1 file changed, 21 insertions(+), 3 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index eed4f4075b3c..0361b119b74e 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -8453,6 +8453,19 @@ static int __alloc_contig_migrate_range(struct compact_control *cc, > return 0; > } > > +static void __alloc_contig_clear_range(unsigned long start_pfn, > + unsigned long end_pfn) > +{ > + unsigned long pfn; > + > + for (pfn = start_pfn; pfn < end_pfn; pfn += MAX_ORDER_NR_PAGES) { > + cond_resched(); > + kernel_init_free_pages(pfn_to_page(pfn), > + min_t(unsigned long, end_pfn - pfn, > + MAX_ORDER_NR_PAGES)); In weird cases, we might cross a MAX_ORDER - 1 block here. I'll fix that. -- Thanks, David / dhildenb