Subject: Re: PPC: Don't sync timebase when inside VM

From: Scott Wood <[email-masked]>
Date: Mon, 22 Jul 2013 17:19:08 -0500

On Fri, Mar 02, 2012 at 03:12:33PM +0100, Alexander Graf wrote:
> When running inside a virtual machine, we can not modify timebase, so
> let's just not call the functions for it then.
> 
> This resolves hangs when booting e500 SMP guests on overcommitted hosts.
> 
> Reported-by: Stuart Yoder <[email-masked]>
> Signed-off-by: Alexander Graf <[email-masked]>
> 
> ---
> arch/powerpc/platforms/85xx/smp.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/85xx/smp.c b/arch/powerpc/platforms/85xx/smp.c
> index ff42490..d4b6c1f 100644
> --- a/arch/powerpc/platforms/85xx/smp.c
> +++ b/arch/powerpc/platforms/85xx/smp.c
> @@ -249,6 +249,13 @@ void __init mpc85xx_smp_init(void)
>  		smp_85xx_ops.cause_ipi = doorbell_cause_ipi;
>  	}
>  
> +	/* When running under a hypervisor, we can not modify tb */
> +	np = of_find_node_by_path("/hypervisor");
> +	if (np) {
> +		smp_85xx_ops.give_timebase = NULL;
> +		smp_85xx_ops.take_timebase = NULL;
> +	}

I'm marking this superseded as we now only set give/take_timebase if a
guts node is present that corresponds to an SMP SoC.  QEMU currently
advertises an mpc8544 guts (which is not SMP) and will eventually move to
a paravirt device with no guts at all.

-Scott