Re: [Xen-devel] [patch] x86: Add a delay between INIT & SIPIs for AP bring-up in X2APIC case

["Wei, Gang" <gang.wei@xxxxxxxxx>]

Keir Fraser wrote on 2011-12-21:
> On 21/12/2011 11:22, "Wei, Gang" <gang.wei@xxxxxxxxx> wrote:
> 
>> Without this delay, Xen could not bring APs up while working with
>> TXT/tboot, because tboot need some time in APs to handle INIT before
>> becoming ready for receiving SIPIs. (this delay was removed as part
>> of c/s 23724 by Tim Deegan)
> 
> Of course Tim will need to review this himself, but a mdelay() right
> here, only on the x2apic path just looks bizarre and fragile.
> 
> Could we make the !x2apic_enabled conditionals that Tim added be
> !(x2apic_enabled || tboot_in_measured_env()) instead? At least that is
> somewhat self-documenting and clearly only affects tboot!

Does below patch make more sense?

diff -r d1aefee43af1 xen/arch/x86/smpboot.c
--- a/xen/arch/x86/smpboot.c    Wed Dec 21 18:51:31 2011 +0800
+++ b/xen/arch/x86/smpboot.c    Wed Dec 21 19:08:57 2011 +0800
@@ -463,6 +463,10 @@ static int wakeup_secondary_cpu(int phys
             send_status = apic_read(APIC_ICR) & APIC_ICR_BUSY;
         } while ( send_status && (timeout++ < 1000) );
     }
+    else if ( tboot_in_measured_env() )
+    {
+        udelay(10);
+    }

     /*
      * Should we send STARTUP IPIs ?

Jimmy

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