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Date:   Fri, 28 Aug 2020 20:29:24 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Anchal Agarwal <anchalag@...zon.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        "Kamata, Munehisa" <kamatam@...zon.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        roger.pau@...rix.com, Jens Axboe <axboe@...nel.dk>,
        David Miller <davem@...emloft.net>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Eduardo Valentin <eduval@...zon.com>,
        "Singh, Balbir" <sblbir@...zon.com>,
        xen-devel@...ts.xenproject.org,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        netdev <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH v3 00/11] Fix PM hibernation in Xen guests

On Fri, Aug 28, 2020 at 8:26 PM Anchal Agarwal <anchalag@...zon.com> wrote:
>
> On Fri, Aug 21, 2020 at 10:22:43PM +0000, Anchal Agarwal wrote:
> > Hello,
> > This series fixes PM hibernation for hvm guests running on xen hypervisor.
> > The running guest could now be hibernated and resumed successfully at a
> > later time. The fixes for PM hibernation are added to block and
> > network device drivers i.e xen-blkfront and xen-netfront. Any other driver
> > that needs to add S4 support if not already, can follow same method of
> > introducing freeze/thaw/restore callbacks.
> > The patches had been tested against upstream kernel and xen4.11. Large
> > scale testing is also done on Xen based Amazon EC2 instances. All this testing
> > involved running memory exhausting workload in the background.
> >
> > Doing guest hibernation does not involve any support from hypervisor and
> > this way guest has complete control over its state. Infrastructure
> > restrictions for saving up guest state can be overcome by guest initiated
> > hibernation.
> >
> > These patches were send out as RFC before and all the feedback had been
> > incorporated in the patches. The last v1 & v2 could be found here:
> >
> > [v1]: https://lkml.org/lkml/2020/5/19/1312
> > [v2]: https://lkml.org/lkml/2020/7/2/995
> > All comments and feedback from v2 had been incorporated in v3 series.
> >
> > Known issues:
> > 1.KASLR causes intermittent hibernation failures. VM fails to resumes and
> > has to be restarted. I will investigate this issue separately and shouldn't
> > be a blocker for this patch series.
> > 2. During hibernation, I observed sometimes that freezing of tasks fails due
> > to busy XFS workqueuei[xfs-cil/xfs-sync]. This is also intermittent may be 1
> > out of 200 runs and hibernation is aborted in this case. Re-trying hibernation
> > may work. Also, this is a known issue with hibernation and some
> > filesystems like XFS has been discussed by the community for years with not an
> > effectve resolution at this point.
> >
> > Testing How to:
> > ---------------
> > 1. Setup xen hypervisor on a physical machine[ I used Ubuntu 16.04 +upstream
> > xen-4.11]
> > 2. Bring up a HVM guest w/t kernel compiled with hibernation patches
> > [I used ubuntu18.04 netboot bionic images and also Amazon Linux on-prem images].
> > 3. Create a swap file size=RAM size
> > 4. Update grub parameters and reboot
> > 5. Trigger pm-hibernation from within the VM
> >
> > Example:
> > Set up a file-backed swap space. Swap file size>=Total memory on the system
> > sudo dd if=/dev/zero of=/swap bs=$(( 1024 * 1024 )) count=4096 # 4096MiB
> > sudo chmod 600 /swap
> > sudo mkswap /swap
> > sudo swapon /swap
> >
> > Update resume device/resume offset in grub if using swap file:
> > resume=/dev/xvda1 resume_offset=200704 no_console_suspend=1
> >
> > Execute:
> > --------
> > sudo pm-hibernate
> > OR
> > echo disk > /sys/power/state && echo reboot > /sys/power/disk
> >
> > Compute resume offset code:
> > "
> > #!/usr/bin/env python
> > import sys
> > import array
> > import fcntl
> >
> > #swap file
> > f = open(sys.argv[1], 'r')
> > buf = array.array('L', [0])
> >
> > #FIBMAP
> > ret = fcntl.ioctl(f.fileno(), 0x01, buf)
> > print buf[0]
> > "
> >
> > Aleksei Besogonov (1):
> >   PM / hibernate: update the resume offset on SNAPSHOT_SET_SWAP_AREA
> >
> > Anchal Agarwal (4):
> >   x86/xen: Introduce new function to map HYPERVISOR_shared_info on
> >     Resume
> >   x86/xen: save and restore steal clock during PM hibernation
> >   xen: Introduce wrapper for save/restore sched clock offset
> >   xen: Update sched clock offset to avoid system instability in
> >     hibernation
> >
> > Munehisa Kamata (5):
> >   xen/manage: keep track of the on-going suspend mode
> >   xenbus: add freeze/thaw/restore callbacks support
> >   x86/xen: add system core suspend and resume callbacks
> >   xen-blkfront: add callbacks for PM suspend and hibernation
> >   xen-netfront: add callbacks for PM suspend and hibernation
> >
> > Thomas Gleixner (1):
> >   genirq: Shutdown irq chips in suspend/resume during hibernation
> >
> >  arch/x86/xen/enlighten_hvm.c      |   7 +++
> >  arch/x86/xen/suspend.c            |  63 ++++++++++++++++++++
> >  arch/x86/xen/time.c               |  15 ++++-
> >  arch/x86/xen/xen-ops.h            |   3 +
> >  drivers/block/xen-blkfront.c      | 122 ++++++++++++++++++++++++++++++++++++--
> >  drivers/net/xen-netfront.c        |  96 +++++++++++++++++++++++++++++-
> >  drivers/xen/events/events_base.c  |   1 +
> >  drivers/xen/manage.c              |  46 ++++++++++++++
> >  drivers/xen/xenbus/xenbus_probe.c |  96 +++++++++++++++++++++++++-----
> >  include/linux/irq.h               |   2 +
> >  include/xen/xen-ops.h             |   3 +
> >  include/xen/xenbus.h              |   3 +
> >  kernel/irq/chip.c                 |   2 +-
> >  kernel/irq/internals.h            |   1 +
> >  kernel/irq/pm.c                   |  31 +++++++---
> >  kernel/power/user.c               |   7 ++-
> >  16 files changed, 464 insertions(+), 34 deletions(-)
> >
> > --
> > 2.16.6
> >
> A gentle ping on the series in case there is any more feedback or can we plan to
> merge this? I can then send the series with minor fixes pointed by tglx@

Some more time, please!

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