From mboxrd@z Thu Jan  1 00:00:00 1970
From: Keir Fraser <keir.xen@gmail.com>
Subject: Re: [PATCH] x86: don't pass negative time to
	gtime_to_gtsc() (try 2)
Date: Mon, 10 Jun 2013 13:23:46 +0100
Message-ID: <CDDB83E2.290BD%keir.xen@gmail.com>
References: <51B5DF9802000078000DCA20@nat28.tlf.novell.com>
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To: Jan Beulich <JBeulich@suse.com>, xen-devel <xen-devel@lists.xen.org>
Cc: Tim Deegan <tim@xen.org>, Keir Fraser <keir@xen.org>
List-Id: xen-devel@lists.xenproject.org

On 10/06/2013 13:15, "Jan Beulich" <JBeulich@suse.com> wrote:

> This mostly reverts commit eb60be3d ("x86: don't pass negative time to
> gtime_to_gtsc()") and instead corrects __update_vcpu_system_time()'s
> handling of this_cpu(cpu_time).stime_local_stamp dating back before the
> start of a HVM guest (which would otherwise lead to a negative value
> getting passed to gtime_to_gtsc(), causing scale_delta() to produce
> meaningless output).
> 
> Flushing the value to zero was wrong, and printing a message for
> something that can validly happen wasn't very useful either.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Acked-by: Keir Fraser <keir@xen.org>

> 
> --- a/xen/arch/x86/time.c
> +++ b/xen/arch/x86/time.c
> @@ -823,16 +823,13 @@ static void __update_vcpu_system_time(st
>              struct pl_time *pl = &v->domain->arch.hvm_domain.pl_time;
>  
>              stime += pl->stime_offset + v->arch.hvm_vcpu.stime_offset;
> -            if ( (s64)stime < 0 )
> -            {
> -                printk(XENLOG_G_WARNING "d%dv%d: bogus time %" PRId64
> -                       " (offsets %" PRId64 "/%" PRId64 ")\n",
> -                       d->domain_id, v->vcpu_id, stime,
> -         pl->stime_offset, v->arch.hvm_vcpu.stime_offset);
> -                stime = 0;
> -            }
> +            if ( stime >= 0 )
> +                tsc_stamp = gtime_to_gtsc(d, stime);
> +            else
> +                tsc_stamp = -gtime_to_gtsc(d, -stime);
>          }
> -        tsc_stamp = gtime_to_gtsc(d, stime);
> +        else
> +            tsc_stamp = gtime_to_gtsc(d, stime);
>      }
>      else
>      {
> 
> 
>