Re: [PATCH 2/2] KVM: x86: Reject KVM_SET_TSC_KHZ VM ioctl when vCPU has been created

["Huang, Kai" <kai.huang@intel.com>]

On Wed, 2025-07-09 at 14:21 +0530, Nikunj A. Dadhania wrote:
> 
> On 7/9/2025 11:08 AM, Kai Huang wrote:
> > Reject the KVM_SET_TSC_KHZ VM ioctl when there's vCPU has already been
> > created.
> 
> Probably the below is clear:
> 
> Reject KVM_SET_TSC_KHZ VM ioctl when vCPUs have been created

Will do.  Thanks.

> 
> > 
> > The VM scope KVM_SET_TSC_KHZ ioctl is used to set up the default TSC
> > frequency that all subsequent created vCPUs use.  It is only intended to
> > be called before any vCPU is created.  Allowing it to be called after
> > that only results in confusion but nothing good.
> > 
> > Note this is an ABI change.  But currently in Qemu (the de facto
> > userspace VMM) only TDX uses this VM ioctl, and it is only called once
> > before creating any vCPU, therefore the risk of breaking userspace is
> > pretty low.
> > 
> > Suggested-by: Sean Christopherson <seanjc@google.com>
> > Signed-off-by: Kai Huang <kai.huang@intel.com>
> 
> Reviewed-by: Nikunj A Dadhania <nikunj@amd.com>

Thanks.  I'll keep you guys RB anyway after adding the mutex.  Let me know
if you are not OK.