Re: [PATCH v3 00/11] Fix PM hibernation in Xen guests

[Anchal Agarwal <anchalag@amazon.com>]

On Fri, Aug 28, 2020 at 08:29:24PM +0200, Rafael J. Wysocki wrote:
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> On Fri, Aug 28, 2020 at 8:26 PM Anchal Agarwal <anchalag@amazon.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!
>
Sure happy to answer any more questions and fix more BUGS!!

--
Anchal