Get physical machine TSC inside VM by rdtsc

[Tao Lyu]

Hello all,

Can anybody help me with this question?

I want to read the timestamp counter using rdtsc inside the KVM virtual machine.

From some blogs, I know I need to disable the following options when starting qemu:

vmx-rdtsc-exit

vmx-rdtscp-exit

tsc-scale

tsc-adjust

vmx-tsc-offset

And enable the following options:

rdtscp

tsc

However, after specifying these options, the rdtsc inside the VM still returns an adjusted counter instead of host counter.

This is the result shown by the vmxcap script:

  Use TSC offsetting                       no
  RDTSC exiting                            no
  Enable RDTSCP                            no
  TSC scaling                              yes

I really appreciate it if anyone could help me. Thank you so much!

Best,

Tao