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Date:   Thu, 28 Apr 2022 14:23:24 +0000
From:   Sebastian Ene <sebastianene@google.com>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org,
        Derek Kiernan <derek.kiernan@xilinx.com>,
        Dragan Cvetic <dragan.cvetic@xilinx.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Rob Herring <robh+dt@kernel.org>, devicetree@vger.kernel.org,
        qperret@google.com, will@kernel.org, maz@kernel.org
Subject: Re: [PATCH v3 2/2] misc: Add a mechanism to detect stalls on guest
 vCPUs
Message-ID: <YmqjXDJCnuEZVGpa@google.com>
References: <20220425134204.149042-1-sebastianene@google.com>
 <20220425134204.149042-3-sebastianene@google.com>
 <YmatGqfEZOSL0Yfg@kroah.com>
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On Mon, Apr 25, 2022 at 04:15:54PM +0200, Greg Kroah-Hartman wrote:
> On Mon, Apr 25, 2022 at 01:42:07PM +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/vm-wdt.c | 207 ++++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 220 insertions(+)
> >  create mode 100644 drivers/misc/vm-wdt.c
> > 
> > diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> > index 2b9572a6d114..71c173e3f064 100644
> > --- a/drivers/misc/Kconfig
> > +++ b/drivers/misc/Kconfig
> > @@ -493,6 +493,18 @@ config OPEN_DICE
> >  
> >  	  If unsure, say N.
> >  
> > +config VM_WATCHDOG
> > +	tristate "Virtual Machine Watchdog"
> > +	select LOCKUP_DETECTOR
> > +	help
> > +	  Detect CPU locks on the 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 exists 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 vm-wdt.
> > +
> >  source "drivers/misc/c2port/Kconfig"
> >  source "drivers/misc/eeprom/Kconfig"
> >  source "drivers/misc/cb710/Kconfig"
> > diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
> > index 2ec634354cf5..fa9d644da5db 100644
> > --- a/drivers/misc/Makefile
> > +++ b/drivers/misc/Makefile
> > @@ -59,3 +59,4 @@ obj-$(CONFIG_XILINX_SDFEC)	+= xilinx_sdfec.o
> >  obj-$(CONFIG_HISI_HIKEY_USB)	+= hisi_hikey_usb.o
> >  obj-$(CONFIG_UID_SYS_STATS)	+= uid_sys_stats.o
> >  obj-$(CONFIG_OPEN_DICE)		+= open-dice.o
> > +obj-$(CONFIG_VM_WATCHDOG)	+= vm-wdt.o

Hi,

> 
> We have no limit on names, why not "vm-watchdog"?
> 

I will update the name to vm-watchdog.

> > \ No newline at end of file
> > diff --git a/drivers/misc/vm-wdt.c b/drivers/misc/vm-wdt.c
> > new file mode 100644
> > index 000000000000..0c4df2fefbb9
> > --- /dev/null
> > +++ b/drivers/misc/vm-wdt.c
> > @@ -0,0 +1,207 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +//
> > +// Virtual watchdog driver.
> > +//  Copyright (C) Google, 2022
> 
> I will need a watchdog maintainer to agree that this is the way to do
> this as I really really do not understand why you can not use that
> subsystem here.
> 

Sure, let me CC Guenter Roeck as he initially helped me with the
feedback on this.

> > +
> > +#include <linux/cpu.h>
> > +#include <linux/init.h>
> > +#include <linux/io.h>
> > +#include <linux/kernel.h>
> > +
> > +#include <linux/device.h>
> > +#include <linux/interrupt.h>
> > +#include <linux/module.h>
> > +#include <linux/nmi.h>
> > +#include <linux/of.h>
> > +#include <linux/of_device.h>
> > +#include <linux/param.h>
> > +#include <linux/percpu.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/slab.h>
> > +
> > +#define DRV_NAME			"vm_wdt"
> 
> KBUILD_MODNAME please
> 

Fixed.

> > +
> > +#define VMWDT_REG_STATUS		(0x00)
> > +#define VMWDT_REG_LOAD_CNT		(0x04)
> > +#define VMWDT_REG_CURRENT_CNT		(0x08)
> > +#define VMWDT_REG_CLOCK_FREQ_HZ		(0x0C)
> > +#define VMWDT_REG_LEN			(0x10)
> > +
> > +#define VMWDT_DEFAULT_CLOCK_HZ		(10)
> > +#define VMWDT_DEFAULT_TIMEOT_SEC	(8)
> > +
> > +struct vm_wdt_s {
> > +	void __iomem *membase;
> > +	u32 clock_freq;
> > +	u32 expiration_sec;
> > +	u32 ping_timeout_ms;
> > +	struct hrtimer per_cpu_hrtimer;
> > +	struct platform_device *dev;
> > +};
> > +
> > +#define vmwdt_reg_write(wdt, reg, value)	\
> > +	iowrite32((value), (wdt)->membase + (reg))
> > +#define vmwdt_reg_read(wdt, reg)		\
> > +	io32read((wdt)->membase + (reg))
> > +
> > +static struct platform_device *virt_dev;
> 
> Only one device in the system?  Please no, use the correct apis and you
> will not have any limits like this.
> 

Can you please explain what do you mean by use the correct APIs ? I
don't think it will be possible or necessary to register multipple
instances of this. 

> > +
> > +static enum hrtimer_restart vmwdt_timer_fn(struct hrtimer *hrtimer)
> > +{
> > +	struct vm_wdt_s *cpu_wdt;
> > +	u32 ticks;
> > +
> > +	cpu_wdt = container_of(hrtimer, struct vm_wdt_s, per_cpu_hrtimer);
> > +	ticks = cpu_wdt->clock_freq * cpu_wdt->expiration_sec;
> > +	vmwdt_reg_write(cpu_wdt, VMWDT_REG_LOAD_CNT, ticks);
> > +	hrtimer_forward_now(hrtimer, ms_to_ktime(cpu_wdt->ping_timeout_ms));
> > +
> > +	return HRTIMER_RESTART;
> > +}
> > +
> > +static void vmwdt_start(void *arg)
> > +{
> > +	u32 ticks;
> > +	struct vm_wdt_s *cpu_wdt = arg;
> > +	struct hrtimer *hrtimer = &cpu_wdt->per_cpu_hrtimer;
> > +
> > +	vmwdt_reg_write(cpu_wdt, VMWDT_REG_CLOCK_FREQ_HZ,
> > +			cpu_wdt->clock_freq);
> > +
> > +	/* Compute the number of ticks required for the watchdog counter
> > +	 * register based on the internal clock frequency and the watchdog
> > +	 * timeout given from the device tree.
> > +	 */
> > +	ticks = cpu_wdt->clock_freq * cpu_wdt->expiration_sec;
> > +	vmwdt_reg_write(cpu_wdt, VMWDT_REG_LOAD_CNT, ticks);
> > +
> > +	/* Enable the internal clock and start the watchdog */
> > +	vmwdt_reg_write(cpu_wdt, VMWDT_REG_STATUS, 1);
> > +
> > +	hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> > +	hrtimer->function = vmwdt_timer_fn;
> > +	hrtimer_start(hrtimer, ms_to_ktime(cpu_wdt->ping_timeout_ms),
> > +		      HRTIMER_MODE_REL_PINNED);
> > +}
> > +
> > +static void vmwdt_stop(void *arg)
> > +{
> > +	struct vm_wdt_s *cpu_wdt = arg;
> > +	struct hrtimer *hrtimer = &cpu_wdt->per_cpu_hrtimer;
> > +
> > +	hrtimer_cancel(hrtimer);
> > +
> > +	/* Disable the watchdog */
> > +	vmwdt_reg_write(cpu_wdt, VMWDT_REG_STATUS, 0);
> > +}
> > +
> > +static int start_watchdog_on_cpu(unsigned int cpu)
> > +{
> > +	struct vm_wdt_s *vm_wdt = platform_get_drvdata(virt_dev);
> > +
> > +	vmwdt_start(this_cpu_ptr(vm_wdt));
> > +	return 0;
> > +}
> > +
> > +static int stop_watchdog_on_cpu(unsigned int cpu)
> > +{
> > +	struct vm_wdt_s *vm_wdt = platform_get_drvdata(virt_dev);
> > +
> > +	vmwdt_stop(this_cpu_ptr(vm_wdt));
> > +	return 0;
> > +}
> > +
> > +static int vmwdt_probe(struct platform_device *dev)
> > +{
> > +	int cpu, ret, err;
> > +	void __iomem *membase;
> > +	struct resource *r;
> > +	struct vm_wdt_s *vm_wdt;
> > +	u32 wdt_clock, wdt_timeout_sec = 0;
> > +
> > +	r = platform_get_resource(dev, IORESOURCE_MEM, 0);
> > +	if (r == NULL)
> > +		return -ENOENT;
> > +
> > +	vm_wdt = alloc_percpu(typeof(struct vm_wdt_s));
> > +	if (!vm_wdt)
> > +		return -ENOMEM;
> > +
> > +	membase = ioremap(r->start, resource_size(r));
> > +	if (!membase) {
> > +		ret = -ENXIO;
> > +		goto err_withmem;
> > +	}
> > +
> > +	virt_dev = dev;
> > +	platform_set_drvdata(dev, vm_wdt);
> > +	if (of_property_read_u32(dev->dev.of_node, "clock", &wdt_clock))
> > +		wdt_clock = VMWDT_DEFAULT_CLOCK_HZ;
> > +
> > +	if (of_property_read_u32(dev->dev.of_node, "timeout-sec",
> > +				 &wdt_timeout_sec))
> > +		wdt_timeout_sec = VMWDT_DEFAULT_TIMEOT_SEC;
> > +
> > +	for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask) {
> > +		struct vm_wdt_s *cpu_wdt = per_cpu_ptr(vm_wdt, cpu);
> > +
> > +		cpu_wdt->membase = membase + cpu * VMWDT_REG_LEN;
> > +		cpu_wdt->clock_freq = wdt_clock;
> > +		cpu_wdt->expiration_sec = wdt_timeout_sec;
> > +		cpu_wdt->ping_timeout_ms = wdt_timeout_sec * MSEC_PER_SEC / 2;
> > +		smp_call_function_single(cpu, vmwdt_start, cpu_wdt, true);
> > +	}
> > +
> > +	err = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
> > +					"virt/watchdog:online",
> > +					start_watchdog_on_cpu,
> > +					stop_watchdog_on_cpu);
> > +	if (err < 0) {
> > +		pr_warn("could not be initialized");
> 
> drivers should never use pr_* calls.  dev_warn() please.
>

Removed this call,

> thanks,
> 
> greg k-h

Thanks,
Sebastian