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Tue, 20 Apr 2021 00:21:24 -0700 (PDT) Received: from [192.168.1.149] ([80.208.71.248]) by smtp.gmail.com with ESMTPSA id p3sm11836507ejd.65.2021.04.20.00.21.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 20 Apr 2021 00:21:23 -0700 (PDT) Subject: Re: [PATCH 1/2] mm: Fix struct page layout on 32-bit systems To: "Matthew Wilcox (Oracle)" , brouer@redhat.com Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, ilias.apalodimas@linaro.org, mcroce@linux.microsoft.com, grygorii.strashko@ti.com, arnd@kernel.org, hch@lst.de, linux-snps-arc@lists.infradead.org, mhocko@kernel.org, mgorman@suse.de References: <20210416230724.2519198-1-willy@infradead.org> <20210416230724.2519198-2-willy@infradead.org> From: Rasmus Villemoes Message-ID: Date: Tue, 20 Apr 2021 09:21:22 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <20210416230724.2519198-2-willy@infradead.org> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 4C051A0000FD X-Stat-Signature: jh7ojmdonx1j39rze8jnhm5re88bazid Received-SPF: none (rasmusvillemoes.dk>: No applicable sender policy available) receiver=imf24; identity=mailfrom; envelope-from=""; helo=mail-ej1-f41.google.com; client-ip=209.85.218.41 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1618903277-526723 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 17/04/2021 01.07, Matthew Wilcox (Oracle) wrote: > 32-bit architectures which expect 8-byte alignment for 8-byte integers > and need 64-bit DMA addresses (arc, arm, mips, ppc) had their struct > page inadvertently expanded in 2019. When the dma_addr_t was added, > it forced the alignment of the union to 8 bytes, which inserted a 4 byte > gap between 'flags' and the union. > > Fix this by storing the dma_addr_t in one or two adjacent unsigned longs. > This restores the alignment to that of an unsigned long, and also fixes a > potential problem where (on a big endian platform), the bit used to denote > PageTail could inadvertently get set, and a racing get_user_pages_fast() > could dereference a bogus compound_head(). > > Fixes: c25fff7171be ("mm: add dma_addr_t to struct page") > Signed-off-by: Matthew Wilcox (Oracle) > --- > include/linux/mm_types.h | 4 ++-- > include/net/page_pool.h | 12 +++++++++++- > net/core/page_pool.c | 12 +++++++----- > 3 files changed, 20 insertions(+), 8 deletions(-) > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 6613b26a8894..5aacc1c10a45 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -97,10 +97,10 @@ struct page { > }; > struct { /* page_pool used by netstack */ > /** > - * @dma_addr: might require a 64-bit value even on > + * @dma_addr: might require a 64-bit value on > * 32-bit architectures. > */ > - dma_addr_t dma_addr; > + unsigned long dma_addr[2]; Shouldn't that member get another name (_dma_addr?) to be sure the buildbots catch every possible (ab)user and get them turned into the new accessors? Sure, page->dma_addr is now "pointer to unsigned long" instead of "dma_addr_t", but who knows if there's a "(long)page->dma_addr" somewhere? Rasmus