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

[Tim Deegan <tim@xxxxxxx>]

At 10:05 +0000 on 27 Dec (1324980346), Wei, Gang wrote:
> > 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?
> 
> First way, code analysis. Tboot VMExitHandler only judge the
> condition, enable trapping SIPI, then VMResume. 10us means more than
> 10,000 cycles in Intel processors supporting TXT, it should be enough
> for this simple code path.

Unless the BIOS does clever things in SMM of course. :)

> Further, I am working on changing the SMP bring-up sequence for tboot
> path from INIT-SIPI-SIPI to MWAIT-memwrite style. It means tboot APs
> will wait in MWAIT loops and Xen BSP will try to write the monitored
> memory to bring APs out of MWAIT loops.

That sounds like a very good idea.

Cheers,

Tim.

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