qemu Machine Type

在创建虚拟机时，可以指定qemu参数：Machine Type，来控制虚机采用的CPU芯片架构。

可选值一般有：i440fx(pc)和q35.具体可以根据命令查看：

[root@10-221-126-2 ~]# /usr/libexec/qemu-kvm -M  help 
Supported machines are:
pc                   RHEL 7.6.0 PC (i440FX + PIIX, 1996) (alias of pc-i440fx-rhel7.6.0)
pc-i440fx-rhel7.6.0  RHEL 7.6.0 PC (i440FX + PIIX, 1996) (default)
pc-i440fx-rhel7.5.0  RHEL 7.5.0 PC (i440FX + PIIX, 1996)
pc-i440fx-rhel7.4.0  RHEL 7.4.0 PC (i440FX + PIIX, 1996)
pc-i440fx-rhel7.3.0  RHEL 7.3.0 PC (i440FX + PIIX, 1996)
pc-i440fx-rhel7.2.0  RHEL 7.2.0 PC (i440FX + PIIX, 1996)
pc-i440fx-rhel7.1.0  RHEL 7.1.0 PC (i440FX + PIIX, 1996)
pc-i440fx-rhel7.0.0  RHEL 7.0.0 PC (i440FX + PIIX, 1996)
rhel6.6.0            RHEL 6.6.0 PC
rhel6.5.0            RHEL 6.5.0 PC
rhel6.4.0            RHEL 6.4.0 PC
rhel6.3.0            RHEL 6.3.0 PC
rhel6.2.0            RHEL 6.2.0 PC
rhel6.1.0            RHEL 6.1.0 PC
rhel6.0.0            RHEL 6.0.0 PC
q35                  RHEL-7.6.0 PC (Q35 + ICH9, 2009) (alias of pc-q35-rhel7.6.0)
pc-q35-rhel7.6.0     RHEL-7.6.0 PC (Q35 + ICH9, 2009)
pc-q35-rhel7.5.0     RHEL-7.5.0 PC (Q35 + ICH9, 2009)
pc-q35-rhel7.4.0     RHEL-7.4.0 PC (Q35 + ICH9, 2009)
pc-q35-rhel7.3.0     RHEL-7.3.0 PC (Q35 + ICH9, 2009)
none                 empty machine

i440fx(pc)和q35区别

Q35-only features

● PCIe “goodies”
– Extended configuration space (MMCFG)
– PCIe native hotplug
– Advanced Error Reporting (AER)
– Alternative Routing-ID Interpretation (ARI)
– Native Power Management
– Function Level Reset (FLR)
– Address Translation Services (ATS) 
● AHCI storage controller
● vIOMMU emulation
● “Secure” Secure Boot

Q35 vs. I440FX

Q35是Intel在2007年9月推出的芯片组，与I440FX/PIIX差别在于：

- Q35 has IOMMU
- Q35 has PCIe
- Q35 has Super I/O chip with LPC interconnect
- Q35 has 12 USB ports
- Q35 SATA vs. PATA

Irq routing

- Q35 PIRQ has 8 pins - PIRQ A-H
- Q35 has two PIC modes – legacy PIC vs I/O APIC
- Q35 runs in I/O APIC mode
- Slots 0-24 are mapped to PIRQ E-H round robin
- PCIe Bus to PIRQ mappings can be programmed
  - Slots 25-31
- Q35 has 8 PCI IRQ vectors available, I440FX/PIIX4 only 2

I440FX/PIIX4 vs. Q35 devices

- AHCI vs. Legacy IDE
- PCI addresses
- Populate slots using flags
- Default slots

zstack应用

以我们熟知的zstack平台为例，创建虚机时的参数一般为：

CreateVmInstance
zoneUuid=05ea6bfe990e466c90614659125fd6b6
clusterUuid=24082bdb1c8b424bab6b9369f80cd465
cpuNum=8
defaultL3NetworkUuid=2fe41b60a82948bab4c317475d235ec9
hostUuid=3823dad8ffa6408ca2bde58fbd8ff0c3
imageUuid=f55dbdcd39f84ee7b0b7e65d3f44b405
l3NetworkUuids=2fe41b60a82948bab4c317475d235ec9
memorySize=8589934592
name=zsytest1
systemTags=vmMachineType::q35

其中 systemTags=vmMachineType::q35参数即可指定qemu-kvm创建的参数中有关Machine Type的指定。

默认为i440fx(pc)

一般情况下legacy启动的基于x86_64CPU架构的虚机，不需要指定systemTags=vmMachineType参数，machine_type为pc:

...
  <os>
    <type arch='x86_64' machine='pc-i440fx-rhel7.6.0'>hvm</type>
    <bootmenu enable='yes'/>
    <smbios mode='sysinfo'/>
  </os>
...

q35

设置为q35时有几种情况：

1. CPU架构为'aarch64', 'mips64el',此时boot mode必须为UEFI（在项目中遇到的ARM架构的zstack）
2. CPU架构为'x86_64',此时boot mode为UEFI(这是实验出来的，尚未找到具体代码)
3. zstack mimi版本需要设置（在项目中遇到的）

virt

除了pc/q35之外，还有一种machine_type：virt

Generic ARM system emulation with the virt machine
If you don't care about reproducing the idiosyncrasies of a particular bit of hardware, such as small amount of RAM, no PCI or other hard disk, etc., and just want to run Linux, the best option is to use:

-M virt
**virt is a platform which doesn't correspond to any real hardware and is designed for use in virtual machines.**

It supports PCI, virtio, recent CPUs and large amounts of RAM.

See this tutorial for information on getting 32-bit ARM Debian Linux running on the "virt" board.

For 64-bit ARM "virt" is also the best choice, and there's a tutorial for 64-bit ARM Debian Linux setup too.

The "versatilepb" machine has also often been used as a general-purpose Linux target in the past; its disadvantage is that it has a very old CPU and only 256MB of RAM, but it does at least have PCI and SCSI. You can find a description of how to install Debian on it here (the author of that tutorial has also provided some prebuilt images). You're probably better off using "virt" though.

参考文献

PCIvsPCIe (qemu.org)

PowerPoint Presentation (qemu.org)

Qemu虚拟化之Machine Type - 敏的博客 | Min’s Blog (remimin.github.io)