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([2001:b07:6468:f312:9520:22e6:6416:5c36]) by smtp.gmail.com with ESMTPSA id g1sm2756164wrv.68.2019.09.25.02.29.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 25 Sep 2019 02:29:52 -0700 (PDT) Subject: Re: [PATCH v4 0/8] Introduce the microvm machine type To: Gerd Hoffmann References: <20190924124433.96810-1-slp@redhat.com> <87h850ssnb.fsf@redhat.com> <20190925091225.bx4c4x2o6qgydidj@sirius.home.kraxel.org> From: Paolo Bonzini Openpgp: preference=signencrypt Message-ID: <8fa274c8-6bb7-bf88-7715-bb23f5dfb7de@redhat.com> Date: Wed, 25 Sep 2019 11:29:51 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190925091225.bx4c4x2o6qgydidj@sirius.home.kraxel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Pankaj Gupta , mtosatti@redhat.com, ehabkost@redhat.com, Sergio Lopez , mst@redhat.com, lersek@redhat.com, David Hildenbrand , qemu-devel@nongnu.org, kvm@vger.kernel.org, imammedo@redhat.com, philmd@redhat.com, rth@twiddle.net Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 25/09/19 11:12, Gerd Hoffmann wrote: > Hi, > >> If you want to add hotplug to microvm, you can reuse the existing code >> for CPU and memory hotplug controllers, and write drivers for them in >> Linux's drivers/platform. The drivers would basically do what the ACPI >> AML tells the interpreter to do. > > How would the linux kernel detect those devices? > > I guess that wouldn't be ACPI, seems everyone wants avoid it[1]. > > So device tree on x86? Something else? Yes, device tree would be great. > [1] Not clear to me why, some minimal ACPI tables listing our > devices (isa-serial, fw_cfg, ...) doesn't look unreasonable > to me. It's not, but ACPI is dog slow and half of the boot time is cut if you remove it. > We could also make virtio-mmio discoverable that way. True, but the simplest way to plumb virtio-mmio into ACPI would be taking the device tree properties and representing them as _DSD[1]. So at this point it's just as easy to use directly the device tree. Paolo [1] https://kernel-recipes.org/en/2015/talks/representing-device-tree-peripherals-in-acpi/