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Message-ID: <YmqjXDJCnuEZVGpa@google.com>
Date: Thu, 28 Apr 2022 14:23:24 +0000
From: Sebastian Ene <sebastianene@...gle.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org,
Derek Kiernan <derek.kiernan@...inx.com>,
Dragan Cvetic <dragan.cvetic@...inx.com>,
Arnd Bergmann <arnd@...db.de>,
Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
qperret@...gle.com, will@...nel.org, maz@...nel.org
Subject: Re: [PATCH v3 2/2] misc: Add a mechanism to detect stalls on guest
vCPUs
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@...gle.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
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