Re: port-amd64/55543: PVHVM fails to attach hypervisor bus on Amazon EC2 t2.micro

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

The following reply was made to PR port-amd64/55543; it has been noted by GNATS.

From: Manuel Bouyer <bouyer%antioche.eu.org@localhost>
To: Jared McNeill <jmcneill%invisible.ca@localhost>
Cc: gnats-bugs%netbsd.org@localhost, port-amd64-maintainer%netbsd.org@localhost,
        gnats-admin%netbsd.org@localhost, netbsd-bugs%netbsd.org@localhost
Subject: Re: port-amd64/55543: PVHVM fails to attach hypervisor bus on Amazon
 EC2 t2.micro
Date: Mon, 7 Sep 2020 12:51:28 +0200

 On Sun, Sep 06, 2020 at 02:50:32PM -0300, Jared McNeill wrote:
 > On Sun, 6 Sep 2020, Manuel Bouyer wrote:
 > 
 > > On Sun, Sep 06, 2020 at 02:31:23PM +0200, Manuel Bouyer wrote:
 > > > Unfortunably with Xen 4.2.5 it boots. Also, xencons is present.
 > > > 
 > > > Can you enter ddb when it's hung ? if so, can you see where the Xen-related
 > > > threads are waiting ?
 > > 
 > > Also, enabling the DPRINTK macro in xenbus/xenbus_probe.c could give
 > > hints.
 > 
 > I don't see any output from DPRINTK so I guess we are hung before the thread
 > had an opportunity to run. Unfortunately console input is not supported on
 > EC2 so I can't get to ddb.
 
 OK, so we have to make guesses.
 acpicpu0 is attached via config_defer() so I guess it doens't need
 threads to be running. On my test systems, after acpicpu0 there are
 xen devices and uhub0.
 Maybe the clock isn't fully functionnal ? Can you try commenting out
 the delay_func/x86_initclock_func override in xen_hvm_init() (carefull,
 there is also this code in init_xen_early(), this one isn't used
 for HVM).
 
 --- xen/hypervisor.c.orig	2020-09-07 12:48:12.005563460 +0200
 +++ xen/hypervisor.c	2020-09-07 12:46:25.405240796 +0200
 @@ -438,8 +438,10 @@
  		xen_start_info.console.domU.evtchn = xen_hvm_param.value;
  	}
  
 +#if 0
  	delay_func = x86_delay = xen_delay;
  	x86_initclock_func = xen_initclocks;
 +#endif
  
  	vm_guest = VM_GUEST_XENPVHVM; /* Be more specific */
  	return 1;
 
 -- 
 Manuel Bouyer <bouyer%antioche.eu.org@localhost>
      NetBSD: 26 ans d'experience feront toujours la difference
 --