Re: [PATCH 4/6] KVM: SVM: Propagate requested TSC frequency on vcpu init

[Avi Kivity <avi@redhat.com>]

On 03/24/2011 12:21 PM, Joerg Roedel wrote:
> On Thu, Mar 24, 2011 at 12:04:13PM +0200, Avi Kivity wrote:
> >  On 03/24/2011 09:40 AM, Joerg Roedel wrote:
> >>  This patch implements the propagation of the VM
> >>  virtual_tsc_khz into each vcpu data-structure to enable the
> >>  tsc-scaling feature.
> >>    static void svm_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
> >>    {
> >>    	struct vcpu_svm *svm = to_svm(vcpu);
> >>  @@ -1093,6 +1123,9 @@ static struct kvm_vcpu *svm_create_vcpu(struct kvm *kvm, unsigned int id)
> >>    	if (err)
> >>    		goto free_svm;
> >>
> >>  +	if (!svm_vcpu_init_tsc(kvm, svm))
> >>  +		goto uninit;
> >>  +
> >
> >  Need to set err.
> >
> >  I'm not really happy about failing on vcpu creation.  Prefer to fail
> >  when setting the frequency.
>
> Yes, in theory this shouldn't happen anyway because wrong frequencies
> are catched when setting them via the ioctl. This is just another check,
> but it should probably be turned into a BUG_ON in svm_vcpu_init_tsc()
> because it is a bug that userspace could set an invalid khz value.

Yes, I saw later.  But BUG_ON() is too dangerous - if the checks don't 
exactly match a malicious user could cause a DOS.

We can just avoid setting the scale and run with the host tsc frequency.

-- 
error compiling committee.c: too many arguments to function