Hi Sebastian, Thanks for working on this and apologies it's taken so long for me to review your changes. On Fri, Jul 01, 2022 at 02:40:14PM +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 is > an emulated MMIO device which is part of the KVM virtual machine > monitor and this part accounts for lost time by looking at the > /proc/{}/task/{}/stat entries. > > Signed-off-by: Sebastian Ene <sebastianene@xxxxxxxxxx> > --- > drivers/misc/Kconfig | 13 ++ > drivers/misc/Makefile | 1 + > drivers/misc/vcpu_stall_detector.c | 212 +++++++++++++++++++++++++++++ > 3 files changed, 226 insertions(+) > create mode 100644 drivers/misc/vcpu_stall_detector.c > > diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig > index 41d2bb0ae23a..83afb41a85cf 100644 > --- a/drivers/misc/Kconfig > +++ b/drivers/misc/Kconfig > @@ -483,6 +483,19 @@ config OPEN_DICE > > If unsure, say N. > > +config VCPU_STALL_DETECTOR > + tristate "VCPU stall detector" I'd probably stick "Guest" in here somewhere, as this driver won't be useful on the host. So something like "Guest vCPU stall detector". > + select LOCKUP_DETECTOR > + depends on OF > + 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. I suggest rewording this along the lines of: When this driver is bound inside a KVM guest, it will periodically "pet" an MMIO stall detector device from each vCPU and allow the host to detect vCPU stalls. To compile this driver as a module, choose M here: the module will be called vcpu_stall_detector. If you do not intend to run this kernel as a guest, say N. but up to you. > 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 70e800e9127f..2be8542616dd 100644 > --- a/drivers/misc/Makefile > +++ b/drivers/misc/Makefile > @@ -60,3 +60,4 @@ obj-$(CONFIG_XILINX_SDFEC) += xilinx_sdfec.o > obj-$(CONFIG_HISI_HIKEY_USB) += hisi_hikey_usb.o > obj-$(CONFIG_HI6421V600_IRQ) += hi6421v600-irq.o > obj-$(CONFIG_OPEN_DICE) += open-dice.o > +obj-$(CONFIG_VCPU_STALL_DETECTOR) += vcpu_stall_detector.o > \ No newline at end of file > diff --git a/drivers/misc/vcpu_stall_detector.c b/drivers/misc/vcpu_stall_detector.c > new file mode 100644 > index 000000000000..039ac54564c1 > --- /dev/null > +++ b/drivers/misc/vcpu_stall_detector.c > @@ -0,0 +1,212 @@ > +// SPDX-License-Identifier: GPL-2.0 This should probably be "GPL-2.0-only" for the avoidance of doubt. > +// > +// VCPU stall detector. > +// Copyright (C) Google, 2022 > + > +#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 REG_STATUS (0x00) > +#define REG_LOAD_CNT (0x04) > +#define REG_CURRENT_CNT (0x08) > +#define REG_CLOCK_FREQ_HZ (0x0C) > +#define REG_LEN (0x10) > + > +#define DEFAULT_CLOCK_HZ (10) > +#define DEFAULT_TIMEOT_SEC (8) TIMEOUT instead of TIMEOT? Generally, I'd probably also prefix these definitions with VCPU_STALL_ or something to avoid the potential for conflicting with the headers. > +struct vm_stall_detect_s { > + void __iomem *membase; > + u32 clock_freq; > + u32 expiration_sec; > + u32 ping_timeout_ms; > + struct hrtimer per_cpu_hrtimer; > + struct platform_device *dev; > +}; > + > +#define vcpu_stall_detect_reg_write(stall_detect, reg, value) \ > + iowrite32((value), (stall_detect)->membase + (reg)) You can use writel_relaxed() here as you don't require ordering guarantees against DMA. > +#define vcpu_stall_detect_reg_read(stall_detect, reg) \ > + io32read((stall_detect)->membase + (reg)) io32read() doesn't exist, but you also don't use this macro so just remove it :) > + > +static struct vm_stall_detect_s __percpu *vm_stall_detect; > + > +static enum hrtimer_restart > +vcpu_stall_detect_timer_fn(struct hrtimer *hrtimer) > +{ > + struct vm_stall_detect_s *cpu_stall_detect; > + u32 ticks; > + > + cpu_stall_detect = container_of(hrtimer, struct vm_stall_detect_s, > + per_cpu_hrtimer); > + ticks = cpu_stall_detect->clock_freq * cpu_stall_detect->expiration_sec; > + vcpu_stall_detect_reg_write(cpu_stall_detect, REG_LOAD_CNT, ticks); > + hrtimer_forward_now(hrtimer, > + ms_to_ktime(cpu_stall_detect->ping_timeout_ms)); > + > + return HRTIMER_RESTART; > +} > + > +static void vcpu_stall_detect_start(void *arg) > +{ > + u32 ticks; > + struct vm_stall_detect_s *cpu_stall_detect = arg; > + struct hrtimer *hrtimer = &cpu_stall_detect->per_cpu_hrtimer; > + > + vcpu_stall_detect_reg_write(cpu_stall_detect, REG_CLOCK_FREQ_HZ, > + cpu_stall_detect->clock_freq); > + > + /* Compute the number of ticks required for the stall detector counter > + * register based on the internal clock frequency and the timeout > + * value given from the device tree. > + */ > + ticks = cpu_stall_detect->clock_freq * > + cpu_stall_detect->expiration_sec; > + vcpu_stall_detect_reg_write(cpu_stall_detect, REG_LOAD_CNT, ticks); > + > + /* Enable the internal clock and start the stall detector */ > + vcpu_stall_detect_reg_write(cpu_stall_detect, REG_STATUS, 1); > + > + hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); > + hrtimer->function = vcpu_stall_detect_timer_fn; > + hrtimer_start(hrtimer, ms_to_ktime(cpu_stall_detect->ping_timeout_ms), > + HRTIMER_MODE_REL_PINNED); > +} > + > +static void vcpu_stall_detect_stop(void *arg) > +{ > + struct vm_stall_detect_s *cpu_stall_detect = arg; > + struct hrtimer *hrtimer = &cpu_stall_detect->per_cpu_hrtimer; > + > + hrtimer_cancel(hrtimer); > + > + /* Disable the stall detector */ > + vcpu_stall_detect_reg_write(cpu_stall_detect, REG_STATUS, 0); > +} > + > +static int start_stall_detector_on_cpu(unsigned int cpu) > +{ > + vcpu_stall_detect_start(this_cpu_ptr(vm_stall_detect)); > + return 0; > +} > + > +static int stop_stall_detector_on_cpu(unsigned int cpu) > +{ > + vcpu_stall_detect_stop(this_cpu_ptr(vm_stall_detect)); > + return 0; > +} > + > +static int vcpu_stall_detect_probe(struct platform_device *dev) > +{ > + int cpu, ret, err; > + void __iomem *membase; > + struct resource *r; > + u32 stall_detect_clock, stall_detect_timeout_sec = 0; > + > + r = platform_get_resource(dev, IORESOURCE_MEM, 0); > + if (r == NULL) > + return -ENODEV; > + > + vm_stall_detect = alloc_percpu(typeof(struct vm_stall_detect_s)); > + if (!vm_stall_detect) > + return -ENOMEM; > + > + membase = ioremap(r->start, resource_size(r)); > + if (!membase) { > + ret = -ENOMEM; > + goto err_withmem; > + } Can you use devm_platform_get_and_ioremap_resource() to avoid calling both platform_get_resource() and ioremap() explicitly? I think the devm_ handling there also means you don't need to worry about the iounmap(), which seems to be missing here anyway. > + > + if (of_property_read_u32(dev->dev.of_node, "clock-frequency", > + &stall_detect_clock)) > + stall_detect_clock = DEFAULT_CLOCK_HZ; > + > + if (of_property_read_u32(dev->dev.of_node, "timeout-sec", > + &stall_detect_timeout_sec)) > + stall_detect_timeout_sec = DEFAULT_TIMEOT_SEC; > + > + for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask) { What prevents CPUs from coming up and down during this loop? I also don't think we should be using 'watchdog_cpumask' here -- that's part of the watchdog core; instead we should either take the mask in the DT description or rely on the device exposing an interface for every CPU in the system. > + struct vm_stall_detect_s *cpu_stall_detect; > + > + cpu_stall_detect = per_cpu_ptr(vm_stall_detect, cpu); > + cpu_stall_detect->membase = membase + cpu * REG_LEN; > + cpu_stall_detect->clock_freq = stall_detect_clock; > + cpu_stall_detect->expiration_sec = stall_detect_timeout_sec; > + > + /* Pet the stall detector at half of its expiration timeout > + * to prevent spurios resets. typo: spurious > + */ > + cpu_stall_detect->ping_timeout_ms = stall_detect_timeout_sec * > + MSEC_PER_SEC / 2; All of these fields are the same for each core apart from the membase, which a CPU can compute locally using its smp_processor_id() so I don't think you need to include these in the per-cpu structure. It would be simpler if you tracked these invariants in a separate structure (either a global static structure or indirected by a per-cpu pointer). Then the only thing left for the per-cpu structure would be the hrtimer. > + smp_call_function_single(cpu, vcpu_stall_detect_start, > + cpu_stall_detect, true); > + } > + > + err = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, > + "virt/vcpu_stall_detector:online", > + start_stall_detector_on_cpu, > + stop_stall_detector_on_cpu); If you drop the "_nocalls" variant then I think you can avoid the explicit previous call to smp_call_function_single() entirely and just rely on the notifiers to do the right thing. That also solves the hotplug race I mentioned. > + if (err < 0) { > + dev_err(&dev->dev, "failed to install cpu hotplug"); > + ret = err; > + goto err_withmem; > + } > + > + return 0; > + > +err_withmem: > + free_percpu(vm_stall_detect); Looks like there's a devm_alloc_percpu() which might make this a bit simpler. > + return ret; > +} > + > +static int vcpu_stall_detect_remove(struct platform_device *dev) > +{ > + int cpu; > + > + for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask) { > + struct vm_stall_detect_s *cpu_stall_detect; > + > + cpu_stall_detect = per_cpu_ptr(vm_stall_detect, cpu); > + smp_call_function_single(cpu, vcpu_stall_detect_stop, > + cpu_stall_detect, true); > + } I don't think you need to cross-call here, and it looks racy again with hotplug; you should be able to do something like: 1. Unregister the hotplug notifier (looks like you're missing this?) 2. Call hrtimer_cancel() for each percpu timer 3. Disable the watchdog for each CPU > + free_percpu(vm_stall_detect); > + vm_stall_detect = NULL; > + return 0; > +} > + > +static const struct of_device_id vcpu_stall_detect_of_match[] = { > + { .compatible = "qemu,vcpu-stall-detector", }, I'm not sure why we're mentioning qemu here; something as boring as "virt" (like you use for the cpuhp notifier) or "dummy" might be better, but given that Rob is happy with the binding then I won't complain further. We can always add extra strings later if we need to. > + {} > +}; > + > +MODULE_DEVICE_TABLE(of, vcpu_stall_detect_of_match); > + > +static struct platform_driver vcpu_stall_detect_driver = { > + .probe = vcpu_stall_detect_probe, > + .remove = vcpu_stall_detect_remove, > + .driver = { > + .name = KBUILD_MODNAME, > + .of_match_table = vcpu_stall_detect_of_match, > + }, > +}; > + > +module_platform_driver(vcpu_stall_detect_driver); > + > +MODULE_LICENSE("GPL"); This needs to be "GPL v2". Will