Re: [PATCH v3 4/7] KVM: x86: nSVM: support PAUSE filter threshold and count when cpu_pm=on
From: Jim Mattson
Date: Wed Mar 09 2022 - 13:36:15 EST
On Tue, Mar 1, 2022 at 6:37 AM Maxim Levitsky <mlevitsk@xxxxxxxxxx> wrote:
>
> Allow L1 to use these settings if L0 disables PAUSE interception
> (AKA cpu_pm=on)
>
> Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
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?