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

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Message-ID: <aSuyZTFXIpVK-VmH@mail-itl>
Date: Sun, 30 Nov 2025 03:56:37 +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 11:47:37AM +0100, Marek Marczykowski-Górecki wrote:
> 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...

Regardless of my other response, those two patches appear to work fine
across domU suspend/resume (both the S3 and s2idle variants).
Note for s2idle I tested it together with other qubes patches:
https://github.com/QubesOS/qubes-linux-kernel/

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

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