Re: [PATCH] KVM: X86: Expose KVM_HINTS_REALTIME in KVM_GET_SUPPORTED_CPUID

[Xiaoyao Li]

On 10/22/2020 9:02 PM, Paolo Bonzini wrote:
> On 22/10/20 03:34, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> >
> > Per KVM_GET_SUPPORTED_CPUID ioctl documentation:
> >
> > This ioctl returns x86 cpuid features which are supported by both the
> > hardware and kvm in its default configuration.
> >
> > A well-behaved userspace should not set the bit if it is not supported.
> >
> > Suggested-by: Jim Mattson <jmattson@xxxxxxxxxx>
> > Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
>
> It's common for userspace to copy all supported CPUID bits to
> KVM_SET_CPUID2, I don't think this is the right behavior for
> KVM_HINTS_REALTIME.

It reminds of X86_FEATURE_WAITPKG, which is added to supported CPUID 
recently as a fix but QEMU exposes it to guest only when "-overcommit 
cpu-pm"

> (But maybe this was discussed already; if so, please point me to the
> previous discussion).
>
> Paolo