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Thu, 4 Oct 2018 13:29:32 +0000 (UTC) Received: from tonnant.bos.jonmasters.org (ovpn-124-32.rdu2.redhat.com [10.10.124.32]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7500C20155E0; Thu, 4 Oct 2018 13:29:31 +0000 (UTC) Subject: Re: [RFC 00/60] Coscheduling for Linux To: =?UTF-8?Q?Jan_H=2e_Sch=c3=b6nherr?= , Ingo Molnar , Peter Zijlstra Cc: linux-kernel@vger.kernel.org References: <20180907214047.26914-1-jschoenh@amazon.de> From: Jon Masters Openpgp: preference=signencrypt Autocrypt: addr=jcm@redhat.com; keydata= xsFNBE6Ll1oBEADNCMsChhQGT2JDjJPzACWwz2LgW9Scrzg7fMuB0QCZUWwYiFn8aSnWbF1D gW8zLaylIUBcoSZNNPQ3S03pHmFtCwCPESaCI/TikHlGA6c996jZzf1zLx/khEecBC1b4pFM VbWzE0RosgXotxu0MCaAp3mLOFWRZJu4BHGuSSuqbT4qfJ1euIN4uSD7+GG5M/O3ERIoYV3Q E8FBUUKKDRXdI8e1fq7iqg59Dq4P922iuhpbdwQRTRQmb+4uuRaJG7PMP5uBtN+Y0umvYK/y ha1kFqunGQ95GTSleD3E5ifjXWAOLjOldl4fxw6a5Z2fbX+uTancr8G85JLzhQp4+0Av5WfV MGe+UCUH8nlfJDzFE0q/oltgXDwE+4Pr9J8NSN4heF8XL5Cn6JnE9d/YvgIGEmyf6J/8WPQ+ nWTqN+VvEkrvn5oHuJOuM16AFRptUFQOJQGCIK/hupwHkR6TjFMA2XLv6CXjAgvWK+z9SAw8 zUFcqDN983qD3pc88lmSgPp7uArmMwBdCEpVayCLvu+M5kzZz9rty73u3Rv1MF0o+Rtdq4uc JLhjCd/FAMTXi5VzkBcuOufgcvqs0kFgloCvdL72+dyowYDJaC8Ir6KNrz3iOk9P56ESY8E3 70/wkoyfVnesrih7ntiqltISotRR7lDp4AD8oskaAcGqKy3AYQARAQABzTdKb24gTWFzdGVy cyAoSm9uYXRoYW4gQ2hhcmxlcyBNYXN0ZXJzKSA8amNtQGtlcm5lbC5vcmc+wsF4BBMBAgAi BQJOi5geAhsDBgsJCAcDAgYVCAIJCgsEFgIDAQIeAQIXgAAKCRDkIJuMiuip0bOWD/9ca9kj mgdy2FFPlb0Cy6gqA0fAKXix27sX56K9FD3HwWgJUC9QpdvqYXxVu1ASK85+FvJKvSs9BdOY uBTtVl29kpVkAkPP+7RIpBQ89Ewhu8wCNFt0ZIcV/c9IivpFDjqSp/eAxrbB9k3IMUYBlDeB vPFnkqI5cxm5Lnl3sJIAI6lby9OJBoVqj38q85JInE2SS2RVM92JvDZFEB3oVryObenG5Fb4 Ugb0DcSC2gKocoa41iBhl3ggz3TjBg9oxSTIFEsRg+AhV0AUWdYCQtQGqng1V1HU38vAACx8 b/NoFnoyjqBA0agECHeC8bpFQHEienP+Hs8K4EhMa79h+EZRqjwzjMvceG85Gsz6yIqcq/3+ TfORU64RZUWzJh/oy0sRbgl5Fj89JIfdqz0YDdYlbNbWhRfV/KOZNdXZWYpqQNcmxPGuHs+Z VkLD84TE5+puOEihNifFFNch0lJSOGwnxged4JJAfJaeZtVp8s+WqCH7rqeCBgetBn32fG/A Tx+EcVi9KAmcrV7opi9uP1ZTQRuRoc95Zia/C9CQFCacnHcQ5JyWf4k6IbDVuGDKqXfAoTmp Jlj0BwarWY9OFtgKpVyFbD0cUz5m/f1G750SjGud/PCmcYGjuDIQdaoE10ZrHjolqbWnWkJl XioO+VRdOFxe9vetIOmPIrNnh6M7fc7BTQROi5daARAAuB7uqbo8oWZlkniNFb/AkTruoUp6 ak+VKLrueaQ5HPVVx4maEUdTsk9mZRlBB6nPXQJAHW/jI0qBqG7hFmhZdRN9Ag2bjGbtuK44 zg/9/dt86n8ASKqu8Q9z1MAslPwm++S9rE02Oif5mlfIl62zlUZhi+ChvaCM+NbZ7u17edo2 0QHnFIQwBqlA29xFzjq9pnzpIe0xxLLuuG8yFe/yWfwAnI1S9Yp5UlDdmF6GMtRroXtmxPud SnMk6K5wvtvY2mkBSc96ug4EYyZfFyUxjnAfcANFCRGnTyF6XxPOBzhKMeYDBu/SIHCyhF2V QFLdSYa0uGSdjqf0hgd09TDa/r7b/pytxJP8+6AZXgQ93JlB+rYfvaLcjypgmPhxXX8UugH8 GaeZGaFZcYvkdsmjE6SWZuM0QfsML9BdSvFT6+Bf0c45rEhO2c8NTyFUsdqC51C1vamReR6R hTc7TFclT++/n29N0ns70edn2lMQ/lDN3uNkQV2xABXFrT1yXdkwN1/7dGnv/4Q+4ihrXJcr y6CP6DJJuIiIRK/x6AVszd4S/2PjmxLiSLpuPLjQ18ZsUJrzqDO7Cc46QTgizVTu+sTEL195 J6quiELm3MB9Ut+6EKzSoJUdNnF/PE/HkzTssQlxZWdO8Yyw3GF2HtHfcyZrW6ZDrZEsnhUC otkmigsAEQEAAcLBXwQYAQIACQUCTouXWgIbDAAKCRDkIJuMiuip0eDBD/9rj2V4zO+DWtY0 HCIn5Cz7HBSw8hRs8orv1QQYUoDZBn5zqIdmjc1SCyNOqTXEEBAnruPE9vxgI0QkuW9uyAWh wL7+rzHZefUx5H2HI1FPGfPL5we37gnpf1S+PhOKobd3KKaiQ0DFqdTqPlZIkGXChIXPF0bG g6HSY/vVHYC4Rqysj/Sw+74nGzJRSisNt60W0LPRcWdbEX4zEvdUJX4YAbUBoEKLOt1VmRXt UeC8hgVOuIxkIVsWlHgVlztn0e0BtOutlR5Lu28D/CWObjHJG6+Kq0PgUiFiHmUFpAhiuPyO nwZOLHdVxflxJBdO8GVRV6GqygZQ8fcg/neDb2waYRBUOROEMzNn5+tG11QBbbYLoBL8eKt3 kgaSfasOaWV5e1+Y6OkZXfjlYqbLkgaFB7ZizUlfsq9sp/aAlAfU5hUISSCaSMinRUQTy6+y +9WGZrrwsWZO7wdq1ccGE6bXFRWhteq5UIJS8cg0m0vnrsv9GddFBeNaF34Ye9hlD05ofBuc PTfbCfHxsndrq+vPPR64uZrh9i7qO/KFZwKns4yGhO78umvHuyinOvEHA2Of1bOP/ohIbTAz VHjokMI4EXkVzgVP9EgwzBwX1PWi6OEFIG0yWltbmFXnn3clTIa/uG1c0VpCRuGtSEtqfC7n yrXvw9qg2waGcnb8WuoS+g== Message-ID: <859c89b3-f43f-c3c7-3064-6bccb3ee65f8@redhat.com> Date: Thu, 4 Oct 2018 09:29:29 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: <20180907214047.26914-1-jschoenh@amazon.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.25 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Thu, 04 Oct 2018 13:29:32 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/7/18 5:39 PM, Jan H. Schönherr wrote: > The collective context switch from one coscheduled set of tasks to another > -- while fast -- is not atomic. If a use-case needs the absolute guarantee > that all tasks of the previous set have stopped executing before any task > of the next set starts executing, an additional hand-shake/barrier needs to > be added. In case nobody else brought it up yet, you're going to need a handshake to strengthen protection against L1TF attacks. Otherwise, there's still a small window where an attack can occur during the reschedule. Perhaps one could then cause this to happen artificially by repeatedly have a VM do some kind of pause/mwait type operation that might do a reschedule. Jon. -- Computer Architect | Sent with my Fedora powered laptop