Re: [patch 7/8] Dont mark TSC unstable due to S4 suspend

[Joerg Roedel <joerg.roedel@amd.com>]

On Fri, Feb 03, 2012 at 03:43:56PM -0200, Marcelo Tosatti wrote:
> +	if (backwards_tsc) {
> +		u64 delta_cyc = max_tsc - local_tsc;
> +		list_for_each_entry(kvm, &vm_list, vm_list) {
> +			kvm_for_each_vcpu(i, vcpu, kvm) {
> +				vcpu->arch.tsc_offset_adjustment += delta_cyc;
> +				vcpu->arch.last_host_tsc = local_tsc;
> +			}
> +
> +			/*
> +			 * We have to disable TSC offset matching.. if you were
> +			 * booting a VM while issuing an S4 host suspend....
> +			 * you may have some problem.  Solving this issue is
> +			 * left as an exercise to the reader.
> +			 */
> +			kvm->arch.last_tsc_nsec = 0;
> +			kvm->arch.last_tsc_write = 0;
> +		}
> +
> +	}
> +	return 0;

This is not going to work when tsc-scaling is enabled. The
adjust_tsc_offset_host() function just scales the offset the same way
the tsc is scaled. But that is broken because the tsc-offset is applied
_after_ the tsc-ratio by scaling hardware. So to get the desired
tsc-value in the guest the offset needs to be scaled in the opposite
direction as the tsc itself. This is rather complicated to implement.

I suggest to drop patch 6/8 and just let adjust_tsc_offset() be using
guest-tsc units. These loops have to be changed then to work with the
guest-tsc instead of the host-tsc.


	Joerg

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