On 3/9/22 19:35, Jim Mattson wrote:
I didn't think pause filtering was virtualizable, since the value of
the internal counter isn't exposed on VM-exit.
On bare metal, for instance, assuming the hypervisor doesn't intercept
CPUID, the following code would quickly trigger a PAUSE #VMEXIT with
the filter count set to 2.
1:
pause
cpuid
jmp 1
Since L0 intercepts CPUID, however, L2 will exit to L0 on each loop
iteration, and when L0 resumes L2, the internal counter will be set to
2 again. L1 will never see a PAUSE #VMEXIT.
How do you handle this?
I would expect that the same would happen on an SMI or a host interrupt.
1:
pause
outl al, 0xb2
jmp 1
In general a PAUSE vmexit will mostly benefit the VM that is pausing, so
having a partial implementation would be better than disabling it
altogether.
Paolo
