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Subject[RFC PATCH 0/2] Introduce a way to adjust CLOCK_BOOTTIME from userspace for VM guests
From: Hikaru Nishida <>

Hi folks,

We'd like to add a sysfs interface that enable us to advance
CLOCK_BOOTTIME from userspace. The use case of this change is that
adjusting guest's CLOCK_BOOTTIME as host suspends to ensure that the
guest can notice the device has been suspended.
We have an application that rely on the difference between
CLOCK_BOOTTIME and CLOCK_MONOTONIC to detect whether the device went
suspend or not. However, the logic did not work well on VM environment
since most VMs are pausing the VM guests instead of actually suspending
them on the host's suspension.
With following patches, we can adjust CLOCK_BOOTTIME without actually
suspending guest and make the app working as intended.
I think this feature is also useful for other VM solutions since there
was no way to do this from userspace.

As far as I checked, it is working as expected but is there any concern
about this change? If so, please let me know.

Hikaru Nishida

Hikaru Nishida (2):
timekeeping: Add timekeeping_adjust_boottime
drivers/virt: introduce CLOCK_BOOTTIME adjustment sysfs interface

drivers/virt/Kconfig | 9 ++++++
drivers/virt/Makefile | 1 +
drivers/virt/boottime_adj.c | 57 +++++++++++++++++++++++++++++++++++++
include/linux/timekeeping.h | 2 ++
kernel/time/timekeeping.c | 26 +++++++++++++++++
5 files changed, 95 insertions(+)
create mode 100644 drivers/virt/boottime_adj.c


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