Re: RFC: VMX: initialize TSC offset relative to vm creation time

[Marcelo Tosatti <mtosatti@redhat.com>]

On Tue, Oct 28, 2008 at 12:36:14PM -0600, David S. Ahern wrote:
> 
> > That is, the fact that KVM does not handle unsynced TSC's on the host is
> > not an argument against this patch which clearly fixes a bug.
> > 
> > Take commit 019960ae9933161c2809fa4ee608ba30d9639fd2 for example.
> > 
> 
> Has anything changed "recently" with the TSC code? Recently here being
> the past 2 months since you first crafted the patch. I ask because in
> the past few runs based on kvm.git trees (e.g., as recently as a pull on
> 10/26), this tsc offset patch no longer fixes the problem.

Hi David,

Can you share showtime output? Works for me.

> 
> The following one does fix the problem with kvm.git pulled on 10/26/08:
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 64e2439..d5da717 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -860,7 +860,7 @@ static void guest_write_tsc(u64 guest_tsc)
>         u64 host_tsc;
> 
>         rdtscll(host_tsc);
> -       vmcs_write64(TSC_OFFSET, guest_tsc - host_tsc);
> +       vmcs_write64(TSC_OFFSET, 0);
>  }
> 
>  /*
> 
> This is the vmx counterpart (or at least to my understanding) to a
> suggestion Ben had for the svm code.
> 
> david