Re: [PATCH kvmtool] kvmtool: expose the TSC Deadline Timer feature to the guest

[Andre Przywara <andre.przywara@arm.com>]

Hi Dimitri,

On 29/09/15 18:00, Dimitri John Ledkov wrote:
> From: Arjan van de Ven <arjan@linux.intel.com>
> 
> with the TSC deadline timer feature, we don't need to calibrate the apic
> timers anymore, which saves more than 100 milliseconds of boot time.
> 
> Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
> Signed-off-by: Dimitri John Ledkov <dimitri.j.ledkov@intel.com>
> ---
>  x86/cpuid.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/x86/cpuid.c b/x86/cpuid.c
> index c3b67d9..1d8bd23 100644
> --- a/x86/cpuid.c
> +++ b/x86/cpuid.c
> @@ -31,6 +31,9 @@ static void filter_cpuid(struct kvm_cpuid2 *kvm_cpuid)
>  			/* Set X86_FEATURE_HYPERVISOR */
>  			if (entry->index == 0)
>  				entry->ecx |= (1 << 31);
> +                        /* Set CPUID_EXT_TSC_DEADLINE_TIMER*/
> +			if (entry->index == 0)
> +				entry->ecx |= (1 << 24);

This can only be enabled if the kernel supports emulation of that
feature (reported via KVM_CAP_TSC_DEADLINE_TIMER)
(cf: Documentation/virtual/kvm/api.txt and respective QEMU code in
target-i386/kvm.c)

Cheers,
Andre.

>  			break;
>  		case 6:
>  			/* Clear X86_FEATURE_EPB */
>