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

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

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().

Paolo

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