linux-kernel - Re: [Xen-devel] [PATCH] xen: Suspend ticks on all CPUs during suspend

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Date:	Mon, 27 Apr 2015 11:33:00 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	<david.vrabel@...rix.com>, <konrad.wilk@...cle.com>
CC:	<xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH] xen: Suspend ticks on all CPUs during suspend

On 08/04/15 19:53, Boris Ostrovsky wrote:
> Commit 77e32c89a711 ("clockevents: Manage device's state separately for
> the core") decouples clockevent device's modes from states. With this
> change when a Xen guest tries to resume, it won't be calling its
> set_mode op which needs to be done on each VCPU in order to make the
> hypervisor aware that we are in oneshot mode.
> 
> This happens because clockevents_tick_resume() (which is an intermediate
> step of resuming ticks on a processor) no longer calls clockevents_set_state()
> and because during suspend clockevent devices on all VCPUs (except for the
> one doing the suspend) are left in ONESHOT state. As result, during resume
> the clockevents state machine will assume that device is already where it
> should be and doesn't need to be updated.
> 
> To avoid this problem we should suspend ticks on all VCPUs during
> suspend.

Sorry for the delay in reviewing this.

> diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c
> index bf19407..2fd9fe8 100644
> --- a/drivers/xen/manage.c
> +++ b/drivers/xen/manage.c
> @@ -131,6 +131,8 @@ static void do_suspend(void)
>  		goto out_resume;
>  	}
>  
> +	xen_arch_suspend();
> +
>  	si.cancelled = 1;

xen_arch_resume() is only called when !si.cancelled but you call
xen_arch_suspend() unconditionally.

David
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