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

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Message-ID: <aSWJSb4OK645r3tk@mail-itl>
Date: Tue, 25 Nov 2025 11:47:37 +0100
From: Marek Marczykowski-Górecki <marmarek@...isiblethingslab.com>
To: Jürgen Groß <jgross@...e.com>
Cc: Jason Andryuk <jason.andryuk@....com>,
	Stefano Stabellini <sstabellini@...nel.org>,
	Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
	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 Tue, Nov 25, 2025 at 09:20:55AM +0100, Jürgen Groß wrote:
> 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.

Sure, but I can't promise it will be this week, I have some deadlines to
meet...

> 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 = {
> 






-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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