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

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

Tim Deegan wrote on 2011-12-22:
> At 12:29 +0000 on 21 Dec (1324470582), Wei, Gang 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)
> 
> It was removed because I was seeing the opposite problem -- if there
> was a delay, the AP did not come up.  Unfortunately I don;'t have
> sucah a machine available any more, so I can't check whether this breaks boot 
> there.
> 
> Is this something that can be fixed in tboot?  If not, than this patch
> is OK, provided it gets a code comment explaining _why_ tboot needs the delay.

First, Linux kernel always place a delay between INIT & SIPIs.

Second, with tboot AP is actually spinning in a mini-guest before receiving 
INIT, upon receiving INIT ipi, AP need time to VMExit, update VMCS to tracking 
SIPIs and VMResume. After that SIPI is able to be trapped by APs. This is MUST 
if giving no change to current AP bring-up method(INIT-SIPI-SIPI) for tboot.

I have provided a resent patch with code comment in a previous reply.

Jimmy

> 
> Cheers,
> 
> Tim.
> 
>> 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 20:26:39 2011 +0800
>> @@ -42,6 +42,7 @@
>>  #include <asm/msr.h> #include <asm/mtrr.h> #include <asm/time.h>
>>  +#include <asm/tboot.h> #include <mach_apic.h> #include
>>  <mach_wakecpu.h> #include <smpboot_hooks.h>
>> @@ -463,6 +464,10 @@ 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 ?

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