[Xen-devel] Re: x2APIC emulation for HVM guest

["Yang, Sheng" <sheng.yang@xxxxxxxxx>]

On Thursday 02 December 2010 14:44:05 Paolo Bonzini wrote:
> On 12/02/2010 07:23 AM, Yang, Sheng wrote:
> > On Thursday 02 December 2010 13:48:15 Paolo Bonzini wrote:
> >> On 12/02/2010 06:43 AM, Yang, Sheng wrote:
> >>> I think we can do it step by step. This patch is big enough.
> >> 
> >> Yes, I agree it can go in as a separate patch.
> >> 
> >>> I'd like to work the direct EOI patch out, but I am thinking about how
> >>> to test it...
> >> 
> >> Maybe you can run Xen inside an HVM guest, forcing x2apic mode to be
> >> enabled?  You do not need nested VMX if you only run PV guests in the
> >> guest hypervisor.
> > 
> > I don't know how much work need to be done for this, and if it's worth to
> > do for something was not be used in practice(if it would be used in
> > practice, then it would be easy for us to test)...
> 
> Maybe it's as easy as this:
> 
> diff --git a/xen/arch/x86/genapic/x2apic.c b/xen/arch/x86/genapic/x2apic.c
> --- a/xen/arch/x86/genapic/x2apic.c
> +++ b/xen/arch/x86/genapic/x2apic.c
> @@ -41,13 +41,13 @@ int x2apic_cmdline_disable(void)
>  static int probe_x2apic_phys(void)
>  {
>      return x2apic && x2apic_phys && x2apic_is_available() &&
> -        iommu_supports_eim();
> +        1;
>  }
> 
>  static int probe_x2apic_cluster(void)
>  {
>      return x2apic && !x2apic_phys && x2apic_is_available() &&
> -        iommu_supports_eim();
> +        1;
>  }
> 
>  const struct genapic apic_x2apic_phys = {
> 
> The original Xen x2apic code was not conditional on iommu_supports_eim().

I didn't mean this part. I am just not sure if xen can run as HVM guest 
smoothly...

Would check that later.

--
regards
Yang, Sheng

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