From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: mx.groups.io; dkim=missing; spf=pass (domain: redhat.com, ip: 209.132.183.28, mailfrom: lersek@redhat.com) Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by groups.io with SMTP; Thu, 22 Aug 2019 11:00:00 -0700 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id A68EC18C8907; Thu, 22 Aug 2019 17:59:59 +0000 (UTC) Received: from lacos-laptop-7.usersys.redhat.com (unknown [10.36.118.90]) by smtp.corp.redhat.com (Postfix) with ESMTP id 15ECD5D6A7; Thu, 22 Aug 2019 17:59:30 +0000 (UTC) Subject: Re: [edk2-rfc] [edk2-devel] CPU hotplug using SMM with QEMU+OVMF To: Paolo Bonzini , "Kinney, Michael D" , "rfc@edk2.groups.io" , "Yao, Jiewen" Cc: Alex Williamson , "devel@edk2.groups.io" , qemu devel list , Igor Mammedov , "Chen, Yingwen" , "Nakajima, Jun" , Boris Ostrovsky , Joao Marcal Lemos Martins , Phillip Goerl References: <8091f6e8-b1ec-f017-1430-00b0255729f4@redhat.com> <74D8A39837DF1E4DA445A8C0B3885C503F75B680@shsmsx102.ccr.corp.intel.com> <047801f8-624a-2300-3cf7-1daa1395ce59@redhat.com> <99219f81-33a3-f447-95f8-f10341d70084@redhat.com> <6f8b9507-58d0-5fbd-b827-c7194b3b2948@redhat.com> <74D8A39837DF1E4DA445A8C0B3885C503F75FAD3@shsmsx102.ccr.corp.intel.com> <7cb458ea-956e-c1df-33f7-025e4f0f22df@redhat.com> <74D8A39837DF1E4DA445A8C0B3885C503F7600B9@shsmsx102.ccr.corp.intel.com> <20190816161933.7d30a881@x1.home> <74D8A39837DF1E4DA445A8C0B3885C503F761B96@shsmsx102.ccr.corp.intel.com> <35396800-32d2-c25f-b0d0-2d7cd8438687@redhat.com> From: "Laszlo Ersek" Message-ID: Date: Thu, 22 Aug 2019 19:59:23 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.70]); Thu, 22 Aug 2019 17:59:59 +0000 (UTC) Content-Type: text/plain; charset=iso-2022-jp Content-Language: en-US Content-Transfer-Encoding: 7bit On 08/21/19 19:05, Paolo Bonzini wrote: > On 21/08/19 17:48, Kinney, Michael D wrote: >> Perhaps there is a way to avoid the 3000:8000 startup >> vector. >> >> If a CPU is added after a cold reset, it is already in a >> different state because one of the active CPUs needs to >> release it by interacting with the hot plug controller. >> >> Can the SMRR for CPUs in that state be pre-programmed to >> match the SMRR in the rest of the active CPUs? >> >> For OVMF we expect all the active CPUs to use the same >> SMRR value, so a check can be made to verify that all >> the active CPUs have the same SMRR value. If they do, >> then any CPU released through the hot plug controller >> can have its SMRR pre-programmed and the initial SMI >> will start within TSEG. >> >> We just need to decide what to do in the unexpected >> case where all the active CPUs do not have the same >> SMRR value. >> >> This should also reduce the total number of steps. > > The problem is not the SMRR but the SMBASE. If the SMBASE area is > outside TSEG, it is vulnerable to DMA attacks independent of the SMRR. > SMBASE is also different for all CPUs, so it cannot be preprogrammed. The firmware and QEMU could agree on a formula, which would compute the CPU-specific SMBASE from a value pre-programmed by the firmware, and the initial APIC ID of the hot-added CPU. Yes, it would duplicate code -- the calculation -- between QEMU and edk2. While that's not optimal, it wouldn't be a first. Thanks Laszlo