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[80.82.209.135]) by mx.google.com with ESMTP id z25si2141127ejr.144.2019.01.31.04.04.18 for ; Thu, 31 Jan 2019 04:04:18 -0800 (PST) Received-SPF: pass (google.com: domain of daniel@gruss.cc designates 80.82.209.135 as permitted sender) client-ip=80.82.209.135; Authentication-Results: mx.google.com; spf=pass (google.com: domain of daniel@gruss.cc designates 80.82.209.135 as permitted sender) smtp.mailfrom=daniel@gruss.cc Received: from [10.27.152.141] (unknown [129.27.152.126]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: lava@gruss.cc) by mail.gruss.cc (Postfix) with ESMTPSA id 3AC242A008D; Thu, 31 Jan 2019 12:04:17 +0000 (UTC) Subject: Re: [PATCH 2/3] mm/filemap: initiate readahead even if IOCB_NOWAIT is set for the I/O To: Vlastimil Babka , Andrew Morton , Linus Torvalds Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-api@vger.kernel.org, Peter Zijlstra , Greg KH , Jann Horn , Jiri Kosina , Dominique Martinet , Andy Lutomirski , Dave Chinner , Kevin Easton , Matthew Wilcox , Cyril Hrubis , Tejun Heo , "Kirill A . Shutemov" , Jiri Kosina References: <20190130124420.1834-1-vbabka@suse.cz> <20190130124420.1834-3-vbabka@suse.cz> From: Daniel Gruss Openpgp: preference=signencrypt Autocrypt: addr=daniel@gruss.cc; prefer-encrypt=mutual; keydata= mQINBFok/U0BEADLXryCuJ5Y11N5tOGwyRJU4H02+4wrG8cwA6n0yLi7Ff57c/1/MQvCbnEj /Bc9YnujAJJb18QdauUVj9D8AbqDpPk6mR6GUCpeBXLMnzhtK8z/yvNpstwXG7+0J8S7xV7C 7Lht+t75urEjOlB/pL7c0us0ofcXDh5QNfq8jJy5u1hsV+S1JzMC8XAfK6yPfAaOi6K+P1b4 5XAUna6iagIbthivY7ZRa5LLIQFAisrjMHFB1tGklBzm3IxKBowggQJ7zukZHCIFTm3wB2ES SOhmaSvYa7NTOnySAm5WBfmnQ6bbfktFd6D0t+nCo4PVCid6poBr0JuvHIQdPzoUTObSpdBX hNeF+o+ZqnIa0pogddqRA3+PBQ6wqnAm21O8VQNX0sTOSFR0udVURWiZf600l+pY2s+qtxLT 3yFVLIs1sU8qjHcjUtJLSkCw6waM69PCzBeHGxnP6hMdYTwlqatr3OrcfcdH0jNlE3ln05SY 0Emo0zHN2D9Hf1y18iyUu1ygM8rdt48xEJZai3nkw/F/A318Fu98lIXFKBzKFd1uvAc3i59E Y5IVxklQNZhPYq9gUq/unnFmpF5ezeyex0Y+hElUlXGk9YgLvSygsXvIO+T3DpDpVycHIu5k AZ4GC8/YmVgwXRweaMuNeIEnsIKmPCqIQ0fWUMBF90D4C3vcjQARAQABtB5EYW5pZWwgR3J1 c3MgPGRhbmllbEBncnVzcy5jYz6JAk4EEwEIADgCGyMFCwkIBwIGFQgJCgsCBBYCAwECHgEC F4AWIQTczWCjO7iAPF0Z2t17BWSF5qix3QUCW+4oTQAKCRB7BWSF5qix3UuMEACwr9qs7U0R czE25tSDH+hWuewccKhKXOomsMGDULpe9J9HgC2VIGMQkWPRGAn4Yp//9HVPEyIGiBbnSHoO /CxHPJKE5VEtYYHS5MuQ/Zvzyn8wYTpPgxAV8kI5mLNqqlHjgpfbpl0cU59u5WO1sfl9OjfA 08gNqXZqqO0M52lhoDClVDtvYVYh0X6BOjyL+Rau8NHi0Z9yBd6r4adUV9qbees5L2ki22J0 2J7UFrZj0SxVrpcItjCMbIBjIuVBTb0dTxxPoQfbP+VIiuPcPsEWTZNi46Qk6HEM3M2su+XL gqsYVUb/IBpioZXFPOvPtuhtR0rnKpXG3l3ja6KnjIXeWuxuInXi4tf6/NEgcnr3ldO5wgvX a45W3FoF7OVj7Qocj0eRTflRsp7cVWLhcjQZ9nONbvEql0zQjB0cyA3BwK1Rix1c1c4RM7YH G3OvhBr4+RwdAQ2qy2sg4etqlF8xlIhUAXLjXW1uS6DkzGNGZ6TKGQXbUdkhp7I3UD1a+T3v prhj19XWTT44fLQjjPzaWvtsLhvabyoBsKaNPHi7f93A9sVsJ2USY6YrFJ3I8lVrpfH35oGP usrTFY8ClCC6426djynKL9Xc2nyr+VXfcwKZKHtg4AsBsQ6dIt6vhW073Da4QXtxpmeiz0dl MwDLY2LR5Tqc8FPYDv+aQsh6wrkCDQRaJP1NARAA4C+gbA3gw/fRQ4qgnqCnebzS8m1Knc6Q 8v7TXE8wO5DSltiEBRWSTwLfJpBaCEwlZsxPUiOZVv008LW5AiXq6xWiETXxz/6Ao1Qq2T/t 5SY+jEDa8yFTyHZOhh0BxlGMh0iCfb3OJik0bifa/MdXdlEcKIi56IrhZ08voNQBABsLcBuU MWFU8gIY8q7vVWd/i5BlQJs6rWf/DF4xP1flxhXrYtWNCr8tv9t6lYbxvUsqv/4QET87rYaH cSbPEqm3Jvfs3yhvQDfXTA/Ez1pLS4Rg7pyrKtYi/wPJtO26L49I6+u3+Zf7jngpW1QqSOr2 Hwmc9vIr2MOGEEF/a3MrI+Mfh98dMvGJV+PJq2/KQpWYynldE25jdblt7Pv8P0HK3DYrkq2Z QDNbIzMUXB7xb0+P7GJyx5bUr/vwDxdndpVKFKAlMTYNVwuL2o7F0LS2T/xlZqzYx6r/Is8E FU/YprOR6h8W3plxkoGw/DASbE4BnfhxUHMz5DAEWn4cxfCqvZThZuRbjN3eCz40EB0qRI1s IGuoazlzr5D+fr0RQspecPUzZjsyWABxLBB75vqiqnYpXmD/YHsEWveLQQXdhkKM0ugKXSML FzVO7V/87GLvSio8Nf669gvWrIsruT1eh2d58wB4JXh1caz8SUmLbJVRTQByVKnP82Y10jtC f0kAEQEAAYkCNgQYAQgAIAIbDBYhBNzNYKM7uIA8XRna3XsFZIXmqLHdBQJb7ihNAAoJEHsF ZIXmqLHd4KAQAMDkNrhkGpayaxcFJLmeKE+ToC1W9TiWrl6wOzlnJG8bvqVxxLlztiT6nWAR kQzDYPD3/SnlqSaBpqtTR1i7mYon8OfLbWUn60/vNmYAidEx/RvY6BeupkvvPImIupxD0nST otR2/8i824veVZ5Zr2+ZYVWDP4VtDHwSeWgo5hUP41sRXzMJyfKfQ8i+EiD4Cpm2zediO16O gF6fT1kRjKUYiqVJE3X/Cchj7K3wMygtnSXfdIfk3ZskDkmGx/GBnlU5lKHDG5ThrZvE6nZy IIf9ahkGG8VfjpXnpHW5oqRoUTCAEIzFifVcU5Qee0OGbqAfQrJDHjo12RwHRKPvjbLQPQ1c KKJTg69SXiEIR7gbK5irPQJh5VMnvPOblBf9rMVzE6GbZcpNUsd2flPvevAOSCW93hIcXCnt YUd+OhjG3S6550J+3knjJx6xAGDS8OH0EbkmQ3LtEtHJa6y4711PAd/a2kv0fG2jrFy0278Y C0jr8jOPg4mm2jwBkWZQIA9bPWIDICPcnV9ztPKZ5WvrHDCLqynd6xQj+jdmjc/Q778AOMsa xcd9MeVyNOtNTTncuxrl/2M+u0gzE9mR6wrd1jcaeQ1uwtYWc3OyP4oJ9zRiuNf4yNREEUNb Z+a2mlt5YdjgzwusCZzslHJVzE0/58r0APdPafDLJ0p6c3Br Message-ID: Date: Thu, 31 Jan 2019 13:04:16 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20190130124420.1834-3-vbabka@suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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 1/30/19 1:44 PM, Vlastimil Babka wrote: > Close that sidechannel by always initiating readahead on the cache if we > encounter a cache miss for preadv2(RWF_NOWAIT); with that in place, probing > the pagecache residency itself will actually populate the cache, making the > sidechannel useless. I fear this does not really close the side channel. You can time the preadv2 function and infer which path it took, so you just bring it down to the same as using mmap and timing accesses. If I understood it correctly, this patch just removes the advantages of preadv2 over mmmap+access for the attacker. Cheers, Daniel