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From:   Hikaru Nishida <hikalium@chromium.org>
To:     linux-kernel@vger.kernel.org
Cc:     suleiman@google.com, Hikaru Nishida <hikalium@chromium.org>,
        Alexander Graf <graf@amazon.com>,
        Andra Paraschiv <andraprs@amazon.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        John Stultz <john.stultz@linaro.org>,
        Kurt Kanzenbach <kurt@linutronix.de>,
        Linus Walleij <linus.walleij@linaro.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Stephen Boyd <sboyd@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: [RFC PATCH 0/2] Introduce a way to adjust CLOCK_BOOTTIME from userspace for VM guests
Date:   Wed, 10 Feb 2021 19:39:06 +0900
Message-Id: <20210210103908.1720658-1-hikalium@google.com>
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From: Hikaru Nishida <hikalium@chromium.org>


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.

Thanks,
Hikaru Nishida


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

 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

-- 
2.30.0.478.g8a0d178c01-goog