[RFC PATCH v3 11/12] xen: Update sched clock offset to avoid system instability in hibernation

[RFC PATCH v3 11/12] xen: Update sched clock offset to avoid system instability in hibernation

[Anchal Agarwal]

Save/restore xen_sched_clock_offset in syscore suspend/resume during PM
hibernation. Commit '867cefb4cb1012: ("xen: Fix x86 sched_clock() interface
for xen")' fixes xen guest time handling during migration. A similar issue
is seen during PM hibernation when system runs CPU intensive workload.
Post resume pvclock resets the value to 0 however, xen sched_clock_offset
is never updated. System instability is seen during resume from hibernation
when system is under heavy CPU load. Since xen_sched_clock_offset is not
updated, system does not see the monotonic clock value and the scheduler
would then think that heavy CPU hog tasks need more time in CPU, causing
the system to freeze

Signed-off-by: Anchal Agarwal <anchalag@amazon.com>
---
Changes Since V2:
 * New patch to update sched clock offset during hibernation to avoid
   hungups during resume when running a CPU intensive workload
---
 arch/x86/xen/suspend.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/xen/suspend.c b/arch/x86/xen/suspend.c
index dae0f74f5390..7e5275944810 100644
--- a/arch/x86/xen/suspend.c
+++ b/arch/x86/xen/suspend.c
@@ -105,6 +105,8 @@ static int xen_syscore_suspend(void)
 		xen_save_steal_clock(cpu);
 	}
 
+	xen_save_sched_clock_offset();
+
 	xrfp.domid = DOMID_SELF;
 	xrfp.gpfn = __pa(HYPERVISOR_shared_info) >> PAGE_SHIFT;
 
@@ -126,6 +128,12 @@ static void xen_syscore_resume(void)
 
 	pvclock_resume();
 
+	/*
+	 * Restore xen_sched_clock_offset during resume to maintain
+	 * monotonic clock value
+	 */
+	xen_restore_sched_clock_offset();
+
 	/* Nonboot CPUs will be resumed when they're brought up */
 	xen_restore_steal_clock(smp_processor_id());
 
-- 
2.24.1.AMZN

[RFC RESEND PATCH v3 00/12] Enable PM hibernation on guest VMs

[Anchal Agarwal]

Resending this in a more threaded format.
  
Hello,
I am sending out a v3 version of series of patches that implements guest
PM hibernation.
These guests are running on xen hypervisor. The patches had been tested
against mainstream kernel. EC2 instance hibernation feature is provided
to the AWS EC2 customers. PM hibernation uses swap space carved out within
the guest[or can be a separate partition], where hibernation image is
stored and restored from.

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.

This series includes some improvements over RFC series sent last year:
https://lists.xenproject.org/archives/html/xen-devel/2018-06/msg00823.html

Changelog v3:
1. Feedback from V2
2. Introduced 2 new patches for xen sched clock offset fix
3. Fixed pirq shutdown/restore in generic irq subsystem
4. Split save/restore steal clock patches into 2 for better readability

Changelog v2:
1. Removed timeout/request present on the ring in xen-blkfront during blkfront freeze
2. Fixed restoring of PIRQs which was apparently working for 4.9 kernels but not for
newer kernel. [Legacy irqs were no longer restored after hibernation introduced with
this commit "020db9d3c1dc0"]
3. Merged couple of related patches to make the code more coherent and readable
4. Code refactoring
5. Sched clock fix when hibernating guest is under heavy CPU load
Note: Under very rare circumstances we see resume failures with KASLR enabled only
on xen instances.  We are roughly seeing 3% failures [>1000 runs] when testing with
various instance sizes and some workload running on each instance. I am currently
investigating the issue as to confirm if its a xen issue or kernel issue.
However, it should not hold back anyone from reviewing/accepting these patches.

Testing done:
All testing is done for multiple hibernation cycle for 5.4 kernel on EC2.

Testing How to:
---------------
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

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
  genirq: Shutdown irq chips in suspend/resume during hibernation
  xen: Introduce wrapper for save/restore sched clock offset
  xen: Update sched clock offset to avoid system instability in
    hibernation

Munehisa Kamata (7):
  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-netfront: add callbacks for PM suspend and hibernation support
  xen-blkfront: add callbacks for PM suspend and hibernation
  xen/time: introduce xen_{save,restore}_steal_clock
  x86/xen: save and restore steal clock

 arch/x86/xen/enlighten_hvm.c      |   8 ++
 arch/x86/xen/suspend.c            |  72 ++++++++++++++++++
 arch/x86/xen/time.c               |  18 ++++-
 arch/x86/xen/xen-ops.h            |   3 +
 drivers/block/xen-blkfront.c      | 119 ++++++++++++++++++++++++++++--
 drivers/net/xen-netfront.c        |  98 +++++++++++++++++++++++-
 drivers/xen/events/events_base.c  |   1 +
 drivers/xen/manage.c              |  73 ++++++++++++++++++
 drivers/xen/time.c                |  29 +++++++-
 drivers/xen/xenbus/xenbus_probe.c |  99 ++++++++++++++++++++-----
 include/linux/irq.h               |   2 +
 include/xen/xen-ops.h             |   8 ++
 include/xen/xenbus.h              |   3 +
 kernel/irq/chip.c                 |   2 +-
 kernel/irq/internals.h            |   1 +
 kernel/irq/pm.c                   |  31 +++++---
 kernel/power/user.c               |   6 +-
 17 files changed, 533 insertions(+), 40 deletions(-)

-- 
2.24.1.AMZN

[RFC PATCH v3 11/12] xen: Update sched clock offset to avoid system instability in hibernation

[Anchal Agarwal]

Save/restore xen_sched_clock_offset in syscore suspend/resume during PM
hibernation. Commit '867cefb4cb1012: ("xen: Fix x86 sched_clock() interface
for xen")' fixes xen guest time handling during migration. A similar issue
is seen during PM hibernation when system runs CPU intensive workload.
Post resume pvclock resets the value to 0 however, xen sched_clock_offset
is never updated. System instability is seen during resume from hibernation
when system is under heavy CPU load. Since xen_sched_clock_offset is not
updated, system does not see the monotonic clock value and the scheduler
would then think that heavy CPU hog tasks need more time in CPU, causing
the system to freeze

Signed-off-by: Anchal Agarwal <anchalag@amazon.com>
---
 arch/x86/xen/suspend.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/xen/suspend.c b/arch/x86/xen/suspend.c
index dae0f74f5390..7e5275944810 100644
--- a/arch/x86/xen/suspend.c
+++ b/arch/x86/xen/suspend.c
@@ -105,6 +105,8 @@ static int xen_syscore_suspend(void)
 		xen_save_steal_clock(cpu);
 	}
 
+	xen_save_sched_clock_offset();
+
 	xrfp.domid = DOMID_SELF;
 	xrfp.gpfn = __pa(HYPERVISOR_shared_info) >> PAGE_SHIFT;
 
@@ -126,6 +128,12 @@ static void xen_syscore_resume(void)
 
 	pvclock_resume();
 
+	/*
+	 * Restore xen_sched_clock_offset during resume to maintain
+	 * monotonic clock value
+	 */
+	xen_restore_sched_clock_offset();
+
 	/* Nonboot CPUs will be resumed when they're brought up */
 	xen_restore_steal_clock(smp_processor_id());
 
-- 
2.24.1.AMZN