linux-kernel - Re: [PATCH 1/2] xenbus: Use .freeze/.thaw to handle xenbus devices

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Message-ID: <1c991699-51b7-4284-8179-6bc78f8f4eac@suse.com>
Date: Tue, 25 Nov 2025 09:20:55 +0100
From: Jürgen Groß <jgross@...e.com>
To: Jason Andryuk <jason.andryuk@....com>,
 Stefano Stabellini <sstabellini@...nel.org>,
 Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
 Marek Marczykowski-Górecki <marmarek@...isiblethingslab.com>
Cc: Yann Sionneau <yann.sionneau@...es.tech>, xen-devel@...ts.xenproject.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] xenbus: Use .freeze/.thaw to handle xenbus devices

On 19.11.25 23:47, Jason Andryuk wrote:
> The goal is to fix s2idle and S3 for Xen PV devices.  A domain resuming
> from s3 or s2idle disconnects its PV devices during resume.  The
> backends are not expecting this and do not reconnect.
> 
> b3e96c0c7562 ("xen: use freeze/restore/thaw PM events for suspend/
> resume/chkpt") changed xen_suspend()/do_suspend() from
> PMSG_SUSPEND/PMSG_RESUME to PMSG_FREEZE/PMSG_THAW/PMSG_RESTORE, but the
> suspend/resume callbacks remained.
> 
> .freeze/restore are used with hiberation where Linux restarts in a new
> place in the future.  .suspend/resume are useful for runtime power
> management for the duration of a boot.
> 
> The current behavior of the callbacks works for an xl save/restore or
> live migration where the domain is restored/migrated to a new location
> and connecting to a not-already-connected backend.
> 
> Change xenbus_pm_ops to use .freeze/thaw/restore and drop the
> .suspend/resume hook.  This matches the use in drivers/xen/manage.c for
> save/restore and live migration.  With .suspend/resume empty, PV devices
> are left connected during s2idle and s3, so PV devices are not changed
> and work after resume.
> 
> Signed-off-by: Jason Andryuk <jason.andryuk@....com>

Acked-by: Juergen Gross <jgross@...e.com>

Marek, could you please give this patch a try with QubesOS? I think this
patch should be verified not to break your use cases regarding suspend /
resume.


Juergen

> ---
>   drivers/xen/xenbus/xenbus_probe_frontend.c | 4 +---
>   1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/xen/xenbus/xenbus_probe_frontend.c b/drivers/xen/xenbus/xenbus_probe_frontend.c
> index 6d1819269cbe..199917b6f77c 100644
> --- a/drivers/xen/xenbus/xenbus_probe_frontend.c
> +++ b/drivers/xen/xenbus/xenbus_probe_frontend.c
> @@ -148,11 +148,9 @@ static void xenbus_frontend_dev_shutdown(struct device *_dev)
>   }
>   
>   static const struct dev_pm_ops xenbus_pm_ops = {
> -	.suspend	= xenbus_dev_suspend,
> -	.resume		= xenbus_frontend_dev_resume,
>   	.freeze		= xenbus_dev_suspend,
>   	.thaw		= xenbus_dev_cancel,
> -	.restore	= xenbus_dev_resume,
> +	.restore	= xenbus_frontend_dev_resume,
>   };
>   
>   static struct xen_bus_type xenbus_frontend = {


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