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Date:   Tue, 21 Jun 2022 09:44:35 +0100
From:   Marc Zyngier <maz@kernel.org>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Sebastian Ene <sebastianene@google.com>,
        Rob Herring <robh+dt@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Dragan Cvetic <dragan.cvetic@xilinx.com>,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
        will@kernel.org, vdonnefort@google.com,
        Guenter Roeck <linux@roeck-us.net>
Subject: Re: [PATCH v7 2/2] misc: Add a mechanism to detect stalls on guest
 vCPUs
In-Reply-To: <YrGBBFW2d/scKDeN@kroah.com>
References: <20220621080308.3952915-1-sebastianene@google.com>
 <20220621080308.3952915-3-sebastianene@google.com>
 <YrGBBFW2d/scKDeN@kroah.com>
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On 2022-06-21 09:27, Greg Kroah-Hartman wrote:
> On Tue, Jun 21, 2022 at 08:03:09AM +0000, Sebastian Ene wrote:
>> This driver creates per-cpu hrtimers which are required to do the
>> periodic 'pet' operation. On a conventional watchdog-core driver, the
>> userspace is responsible for delivering the 'pet' events by writing to
>> the particular /dev/watchdogN node. In this case we require a strong
>> thread affinity to be able to account for lost time on a per vCPU.
>> 
>> This part of the driver is the 'frontend' which is reponsible for
>> delivering the periodic 'pet' events, configuring the virtual 
>> peripheral
>> and listening for cpu hotplug events. The other part of the driver
>> handles the peripheral emulation and this part accounts for lost time 
>> by
>> looking at the /proc/{}/task/{}/stat entries and is located here:
>> https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3548817
>> 
>> Signed-off-by: Sebastian Ene <sebastianene@google.com>
>> ---
>>  drivers/misc/Kconfig               |  12 ++
>>  drivers/misc/Makefile              |   1 +
>>  drivers/misc/vcpu_stall_detector.c | 222 
>> +++++++++++++++++++++++++++++
>>  3 files changed, 235 insertions(+)
>>  create mode 100644 drivers/misc/vcpu_stall_detector.c
>> 
>> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
>> index 41d2bb0ae23a..e15c85d74c4b 100644
>> --- a/drivers/misc/Kconfig
>> +++ b/drivers/misc/Kconfig
>> @@ -483,6 +483,18 @@ config OPEN_DICE
>> 
>>  	  If unsure, say N.
>> 
>> +config VCPU_STALL_DETECTOR
>> +	tristate "VCPU stall detector"
>> +	select LOCKUP_DETECTOR
>> +	help
>> +	  Detect CPU locks on a kvm virtual machine. This driver relies on
>> +	  the hrtimers which are CPU-binded to do the 'pet' operation. When 
>> a
>> +	  vCPU has to do a 'pet', it exits the guest through MMIO write and
>> +	  the backend driver takes into account the lost ticks for this
>> +	  particular CPU.
>> +	  To compile this driver as a module, choose M here: the
>> +	  module will be called vcpu_stall_detector.
> 
> Should this depend on KVM_GUEST?

Not all architectures have KVM_GUEST, and arm64 has no use for it.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...