Tag: nested

Enable sse on virtual machine(kvm)

Kernel-based Virtual Machine (KVM) has become the defacto hypervisor on GNU/Linux systems it works with a great performance as it utilizes the CPU virtualization extensions Intel VT-x or AMD-V). KVM doesn’t emulate hardware but uses QEMU for this.

Nested Virtual guest

It’s possible to use nested virtualization this makes it possible to run a hypervisor inside a KVM virtual machine.

Verify

To verify if nested virtualization is enabled on your system can check /sys/module/kvm_intel/parameters/nested on Intal systems or /sys/module/kvm_amd/parameters/nested

[staf@ak ~]$ cat /sys/module/kvm_intel/parameters/nested
N
[staf@ak ~]$

Enable

Shutdown all virtual machines

Make sure that there no virtual machines running.

[root@ak ~]# virsh 
Welcome to virsh, the virtualization interactive terminal.

Type:  'help' for help with commands
       'quit' to quit

virsh # list
 Id    Name                           State
----------------------------------------------------

virsh #

Unload KVM

Unload the KVM kernel module.

[root@ak ~]# modprobe -r kvm_intel
[root@ak ~]#

Load KVM and activate nested

Reload the KVM with the nested feature enabled.

[root@ak ~]# modprobe kvm_intel nested=1
[root@ak ~]#

Verify

[root@ak ~]# cat /sys/module/kvm_intel/parameters/nested
Y
[root@ak ~]#

To enable the nested feature permanently create /etc/modprobe.d/kvm_intel.conf

[root@ak ~]# vi /etc/modprobe.d/kvm_intel.conf

and enable the nested option.

options kvm_intel nested=1

Enabling nested virtualization in the virtual machine

When you logon to a virtual machine and verify the virtualization extensions on the cpu the flags aren’t available.

[staf@centos7 ~]$ cat /proc/cpuinfo | grep  -i -E "vmx|svm"
[staf@centos7 ~]$

To enable nested virtualization in a vritual machine you can

  • start virsh and and edit the the virtual machine and change the CPU line to <cpu mode='host-model' check='partial'/>
  • Open virt-manager and select Copy host CPU configuration on the CPU configuration
root@ak ~]# virsh 
Welcome to virsh, the virtualization interactive terminal.

Type:  'help' for help with commands
       'quit' to quit

virsh # list
 Id    Name                           State
----------------------------------------------------
 1     centos7.0                      running

virsh # edit centos7.0

Change the cpu settings

  <features>
    <acpi/>
    <apic/>
    <vmport state='off'/>
  </features>
  <cpu mode='host-model' check='partial'>
    <model fallback='allow'/>
  </cpu>

Shutdown the virtual machine

virsh # reboot centos7.0 
Domain centos7.0 is being rebooted

virsh #

Start the virtual machine

virsh # start centos7.0  
Domain centos7.0 started

While saving the virsh domain xml you might get an error as:

Extra element cpu in interleave

Press i for ignore and start the domain.

Logon to the virtual machine and verify the cpu flags;

[staf@centos7 ~]$ cat /proc/cpuinfo | grep -i vmx
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ss syscall nx pdpe1gb rdtscp lm constant_tsc rep_good nopl xtopology eagerfpu pni pclmulqdq vmx ssse3 fma cx16 pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand hypervisor lahf_lm abm tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid xsaveopt ibpb ibrs arat spec_ctrl
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ss syscall nx pdpe1gb rdtscp lm constant_tsc rep_good nopl xtopology eagerfpu pni pclmulqdq vmx ssse3 fma cx16 pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand hypervisor lahf_lm abm tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid xsaveopt ibpb ibrs arat spec_ctrl
[staf@centos7 ~]$ cat /proc/cpuinfo | grep  -i "vmx|svm"
[staf@centos7 ~]$ cat /proc/cpuinfo | grep  -i -E "vmx|svm"
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ss syscall nx pdpe1gb rdtscp lm constant_tsc rep_good nopl xtopology eagerfpu pni pclmulqdq vmx ssse3 fma cx16 pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand hypervisor lahf_lm abm tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid xsaveopt ibpb ibrs arat spec_ctrl
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ss syscall nx pdpe1gb rdtscp lm constant_tsc rep_good nopl xtopology eagerfpu pni pclmulqdq vmx ssse3 fma cx16 pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand hypervisor lahf_lm abm tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid xsaveopt ibpb ibrs arat spec_ctrl

Nested Function calling in Python

def f1(): 
    X = 88
    def f2(): 
        print(X)
    return f2
action = f1() 
action()

Since f1 is returning f2 so it seems fine when I call f2 as (f1())().

But when I call f2 directly as f2(), it gives error. 

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'f2' is not defined

Can someone explain what is the difference between the function calling of f2 using above 2 ways.

Solution:

The function f2 is local to the scope of function f1. Its name is only valid inside of that function because you defined it there. When you return f2, all you are doing is giving the rest of the program access to the function’s properties, not to its name. The function f1 returns something that prints 88 but does not expose the name f2 to the outer scope.

Calling f2 indirectly through f1()() or action() is perfectly valid because those names are defined in that outer scope. The name f2 is not defined in the outer scope so calling it is a NameError.

acess function in objected, nested inside another function

Im trying to manage a connection instance, using a function to handle idle connection disconnect issues, using mysql database and node.js

At moment, i’ve got following code (coffescript):

mysql = require 'mysql'

handleDisconnect = () ->
  connection = mysql.createConnection
    host: 'localhost'
    user: 'root'
    password: 'passroot'
    database: 'mydb'

  connection.connect (err) ->
    if err
      console.log 'Error connecting to db: ', err
    setTimeout handleDisconnect, 2000

  connection.on 'error', (err) ->
    console.log 'db error', err
    if err.code == 'PROTOCOL_CONNECTION_LOST'
      handleDisconnect()
    else
      throw err

  handleDisconnect.instance = connection

module.exports = handleDisconnect

and

express = require 'express'
router = express.Router()
connection = require('../database')().instance

bcrypt = require 'bcryptjs'

router.post '/', (req, res) ->
  credential = connection.escape req.body.credential
  password = connection.escape req.body.password
  res.send credential+password

module.exports = router

Problem is, when i try to access the route, i get following error:

Cannot read property ‘escape’ of undefined

What am i doing wrong?

Solution:

I believe your issue is that the final line of handleDisconnect is returning the instance, so you’re trying to get the instance from instance, not from handleDisconnect. So you’ll need the function to return itself at the end if you want to access properties on it.

You also want the function to be using the equivalent of “this” (@ in coffeescript) rather than specifically referring to handleDisconnect.

Example code:

mysql = require 'mysql'

handleDisconnect = () ->
  connection = mysql.createConnection
    host: 'localhost'
    user: 'root'
    password: 'passroot'
    database: 'mydb'

  connection.connect (err) ->
    if err
      console.log 'Error connecting to db: ', err
    setTimeout handleDisconnect, 2000

  connection.on 'error', (err) ->
    console.log 'db error', err
    if err.code == 'PROTOCOL_CONNECTION_LOST'
      handleDisconnect()
    else
      throw err

  @instance = connection
  @

module.exports = handleDisconnect

Although I’d personally just do the following, don’t bother with “instance” at all:

  1. Use @connection in your function
  2. Scrap the @instance = connection
  3. Get the function to return itself
  4. Access it with require('../database')().connection.