On Wed, Jul 06, 2022 at 04:21:01PM +0100, Will Deacon wrote: Hi Will, > 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". > I improved the description with your suggesion. > > + 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. > I reworded this, thanks ! > > 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. > I updated the license. > > +// > > +// 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? > I fixed the typo. > Generally, I'd probably also prefix these definitions with VCPU_STALL_ > or something to avoid the potential for conflicting with the headers. > I prefixed the definitions with VCPU_STALL_. > > +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. > I updated it to use writel_relaxed(..) as suggested. > > +#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 :) > I removed this unused definition. > > + > > +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. > Thanks, I updated the code to use the devm_platform_get_and_ioremap_resource(..) API and I modified the Kconfig so that the driver would depend on HAS_IOMEM. > > + > > + 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 > Fixed the typo. > > + */ > > + 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. > I removed the fields which are not needed per-cpu and I only kept the hrtimers. I created a separate global config structure which holds the removed data. > > + 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. > I updated the code to use the cpuhp_setup_state API. > > + 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. > I updated the code to use devm_alloc_percpu(..) and I got rid of the free_percpu(..). > > + 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 > Thanks for pointing our ! I restructured the code on the teardown path. > > + 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. > I used this because I originaly designed this for qemu and then I ported it to crovm. > > + {} > > +}; > > + > > +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". > I think this should stay as is. > Will Thanks for reviewing my code ! Seb