Re: [PATCH] KVM: x86: believe what KVM says about WAITPKG

[Paolo Bonzini]

On 30/06/20 18:07, Maxim Levitsky wrote:
> I think we need to keep some form of this hack, since the kernel doesn't 
> report CPUID_7_0_ECX_WAITPKG via
> KVM_GET_SUPPORTED_CPUID, so for this to work, we need to fix the kernel to 
> report it. 
> But to support older kernels that don't report this bit, we might still need 
> this.
> What do you think?
> 
> Note that kvm_arch_get_supported_cpuid also has a override for what KVM 
> reports about CPUID_EXT_MONITOR
> via KVM_GET_SUPPORTED_CPUID when cpu_pm=on and also does this without 
> checking any conditions,
> and it works because MWAIT is very old feature, and I guess it was the 
> inspiration for the above override
> that we are trying to remove.
> 
> Kernel sadly masks both MWAIT and WAITPKG in KVM_GET_SUPPORTED_CPUID currently
> (it is in kvm_set_cpu_caps)

Right.  We need to use host_cpuid instead of kvm_arch_get_supported_cpuid.

Paolo