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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.12.11 at 04:14, "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)
> 
> Signed-off-by: Gang Wei <gang.wei@xxxxxxxxx>
> Acked-by: Keir Fraser <keir@xxxxxxx>
> Acked-by: Tim Deegan <tim.deegan@xxxxxxxxxx>
> 
> 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  Fri Dec 23 11:01:10 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 +464,18 @@
>              send_status = apic_read(APIC_ICR) & APIC_ICR_BUSY;
>          } while ( send_status && (timeout++ < 1000) );
>      }
> +    else if ( tboot_in_measured_env() )
> +    {
> +        /*
> +         * 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.
> +         *
> +         * While AP is in root mode handling the INIT the CPU will drop
> +         * any SIPIs
> +         */
> +        udelay(10);

So you jumped from 100ms to 10us - how was that value established?
Or in other words, how certain is it that this (or any other) timeout is
sufficient for all current and future systems implementing tboot?

Jan

> +    }
>  
>      /*
>       * Should we send STARTUP IPIs ?




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