> -----Original Message-----
> From: KY Srinivasan
> Sent: Sunday, June 10, 2018 2:54 PM
> To: Sunil Muthuswamy <sunilmut@xxxxxxxxxxxxx>; Haiyang Zhang
> <haiyangz@xxxxxxxxxxxxx>
> Cc: devel@xxxxxxxxxxxxxxxxxxxxxx; Stephen Hemminger
> <sthemmin@xxxxxxxxxxxxx>
> Subject: RE: [PATCH v5] Drivers: HV: Send one page worth of kmsg dump
> over Hyper-V during panic
>
>
>
> > -----Original Message-----
> > From: Sunil Muthuswamy
> > Sent: Friday, June 8, 2018 11:39 AM
> > To: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> > Cc: devel@xxxxxxxxxxxxxxxxxxxxxx; Sunil Muthuswamy
> > <sunilmut@xxxxxxxxxxxxx>; KY Srinivasan <kys@xxxxxxxxxxxxx>; Stephen
> > Hemminger <sthemmin@xxxxxxxxxxxxx>
> > Subject: [PATCH v5] Drivers: HV: Send one page worth of kmsg dump over
> > Hyper-V during panic
> >
> > In the VM mode on Hyper-V, currently, when the kernel panics, an error
> > code and few register values are populated in an MSR and the Hypervisor
> > notified. This information is collected on the host. The amount of
> > information currently collected is found to be limited and not very
> > actionable. To gather more actionable data, such as stack trace, the
> > proposal is to write one page worth of kmsg data on an allocated page
> > and the Hypervisor notified of the page address through the MSR.
> >
> > - Sysctl option to control the behavior, with ON by default.
> >
> > Cc: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
> > Cc: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
> > Signed-off-by: Sunil Muthuswamy <sunilmut@xxxxxxxxxxxxx>
> > ---
> > Changes since v1:
> > - Added a sysctl config option to allow the user to control if panic message
> > should be reported to Hyper-V.
> >
> > Changes since v2:
> > - Addressed comments from Greg KH.
> > - Moved the sysctl config option from 'kernel.hyperv' to 'kernel.' since the
> > likelihood of having many Hyper-V specific sysctl config options seemed
> less
> > and so having a specific dir for Hyper-V seemed unnecessary overhead.
> >
> > Changes since v3:
> > - The feature is only enabled if the capability is supported by the
> hypervisor.
> > This is done by reading the crash control MSR, in addition to the pre-
> existing
> > check for the hypervisor feature using the CPUID.
> >
> > Changes since v4:
> > - Addressed comments from Dexuan Cui: moved the global variable to
> static.
> > ---
> > Documentation/sysctl/kernel.txt | 11 ++++
> > arch/x86/hyperv/hv_init.c | 27 +++++++++
> > arch/x86/include/asm/hyperv-tlfs.h | 5 +-
> > arch/x86/include/asm/mshyperv.h | 1 +
> > drivers/hv/vmbus_drv.c | 116
> > +++++++++++++++++++++++++++++++++++++
> > 5 files changed, 158 insertions(+), 2 deletions(-)
> >
> > diff --git a/Documentation/sysctl/kernel.txt
> > b/Documentation/sysctl/kernel.txt
> > index eded671d..5958503 100644
> > --- a/Documentation/sysctl/kernel.txt
> > +++ b/Documentation/sysctl/kernel.txt
> > @@ -39,6 +39,7 @@ show up in /proc/sys/kernel:
> > - hung_task_check_count
> > - hung_task_timeout_secs
> > - hung_task_warnings
> > +- hyperv_record_panic_msg
> > - kexec_load_disabled
> > - kptr_restrict
> > - l2cr [ PPC only ]
> > @@ -374,6 +375,16 @@ This file shows up if CONFIG_DETECT_HUNG_TASK
> is
> > enabled.
> >
> >
> >
> ==========================================================
> > ====
> >
> > +hyperv_record_panic_msg:
> > +
> > +Controls whether the panic kmsg data should be reported to Hyper-V.
> > +
> > +0: do not report panic kmsg data.
> > +
> > +1: report the panic kmsg data. This is the default behavior.
> > +
> >
> +=========================================================
> > =====
> > +
> > kexec_load_disabled:
> >
> > A toggle indicating if the kexec_load syscall has been disabled. This
> > diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> > index cfecc22..af57162 100644
> > --- a/arch/x86/hyperv/hv_init.c
> > +++ b/arch/x86/hyperv/hv_init.c
> > @@ -395,6 +395,33 @@ void hyperv_report_panic(struct pt_regs *regs,
> long
> > err)
> > }
> > EXPORT_SYMBOL_GPL(hyperv_report_panic);
> >
> > +/**
> > + * hyperv_report_panic_msg - report panic message to Hyper-V
> > + * @pa: physical address of the panic page containing the message
> > + * @size: size of the message in the page
> > + */
> > +void hyperv_report_panic_msg(phys_addr_t pa, size_t size)
> > +{
> > + /*
> > + * P3 to contain the physical address of the panic page & P4 to
> > + * contain the size of the panic data in that page. Rest of the
> > + * registers are no-op when the NOTIFY_MSG flag is set.
> > + */
> > + wrmsrl(HV_X64_MSR_CRASH_P0, 0);
> > + wrmsrl(HV_X64_MSR_CRASH_P1, 0);
> > + wrmsrl(HV_X64_MSR_CRASH_P2, 0);
> > + wrmsrl(HV_X64_MSR_CRASH_P3, pa);
> > + wrmsrl(HV_X64_MSR_CRASH_P4, size);
> > +
> > + /*
> > + * Let Hyper-V know there is crash data available along with
> > + * the panic message.
> > + */
> > + wrmsrl(HV_X64_MSR_CRASH_CTL,
> > + (HV_CRASH_CTL_CRASH_NOTIFY |
> > HV_CRASH_CTL_CRASH_NOTIFY_MSG));
> > +}
> > +EXPORT_SYMBOL_GPL(hyperv_report_panic_msg);
> > +
> > bool hv_is_hyperv_initialized(void)
> > {
> > union hv_x64_msr_hypercall_contents hypercall_msr;
> > diff --git a/arch/x86/include/asm/hyperv-tlfs.h
> > b/arch/x86/include/asm/hyperv-tlfs.h
> > index 416cb0e..76c58af 100644
> > --- a/arch/x86/include/asm/hyperv-tlfs.h
> > +++ b/arch/x86/include/asm/hyperv-tlfs.h
> > @@ -171,9 +171,10 @@
> > #define HV_X64_ENLIGHTENED_VMCS_RECOMMENDED (1 << 14)
> >
> > /*
> > - * Crash notification flag.
> > + * Crash notification flags.
> > */
> > -#define HV_CRASH_CTL_CRASH_NOTIFY (1ULL << 63)
> > +#define HV_CRASH_CTL_CRASH_NOTIFY_MSG BIT_ULL(62)
> > +#define HV_CRASH_CTL_CRASH_NOTIFY BIT_ULL(63)
> >
> > /* MSR used to identify the guest OS. */
> > #define HV_X64_MSR_GUEST_OS_ID 0x40000000
> > diff --git a/arch/x86/include/asm/mshyperv.h
> > b/arch/x86/include/asm/mshyperv.h
> > index b90e796..ac83f2d 100644
> > --- a/arch/x86/include/asm/mshyperv.h
> > +++ b/arch/x86/include/asm/mshyperv.h
> > @@ -262,6 +262,7 @@ void hyperv_init(void);
> > void hyperv_setup_mmu_ops(void);
> > void hyper_alloc_mmu(void);
> > void hyperv_report_panic(struct pt_regs *regs, long err);
> > +void hyperv_report_panic_msg(phys_addr_t pa, size_t size);
> > bool hv_is_hyperv_initialized(void);
> > void hyperv_cleanup(void);
> >
> > diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> > index b10fe26..eec3b235 100644
> > --- a/drivers/hv/vmbus_drv.c
> > +++ b/drivers/hv/vmbus_drv.c
> > @@ -56,6 +56,8 @@ static struct completion probe_event;
> >
> > static int hyperv_cpuhp_online;
> >
> > +static void *hv_panic_page;
> > +
> > static int hyperv_panic_event(struct notifier_block *nb, unsigned long val,
> > void *args)
> > {
> > @@ -1018,6 +1020,75 @@ static void vmbus_isr(void)
> > add_interrupt_randomness(HYPERVISOR_CALLBACK_VECTOR, 0);
> > }
> >
> > +/*
> > + * Boolean to control whether to report panic messages over Hyper-V.
> > + *
> > + * It can be set via /proc/sys/kernel/hyperv/record_panic_msg
> > + */
> > +static int sysctl_record_panic_msg = 1;
> > +
> > +/*
> > + * Callback from kmsg_dump. Grab as much as possible from the end of
> the
> > kmsg
> > + * buffer and call into Hyper-V to transfer the data.
> > + */
> > +static void hv_kmsg_dump(struct kmsg_dumper *dumper,
> > + enum kmsg_dump_reason reason)
> > +{
> > + size_t bytes_written;
> > + phys_addr_t panic_pa;
> > +
> > + /* We are only interested in panics. */
> > + if ((reason != KMSG_DUMP_PANIC) || (!sysctl_record_panic_msg))
> > + return;
> > +
> > + panic_pa = virt_to_phys(hv_panic_page);
> > +
> > + /*
> > + * Write dump contents to the page. No need to synchronize; panic
> > should
> > + * be single-threaded.
> > + */
> > + if (!kmsg_dump_get_buffer(dumper, true, hv_panic_page,
> > + PAGE_SIZE, &bytes_written)) {
> > + pr_err("Hyper-V: Unable to get kmsg data for panic\n");
> > + return;
> > + }
> > +
> > + hyperv_report_panic_msg(panic_pa, bytes_written);
> > +}
> > +
> > +static struct kmsg_dumper hv_kmsg_dumper = {
> > + .dump = hv_kmsg_dump,
> > +};
> > +
> > +static struct ctl_table_header *hv_ctl_table_hdr;
> > +static int zero;
> > +static int one = 1;
> > +
> > +/*
> > + * sysctl option to allow the user to control whether kmsg data should be
> > + * reported to Hyper-V on panic.
> > + */
> > +static struct ctl_table hv_ctl_table[] = {
> > + {
> > + .procname = "hyperv_record_panic_msg",
> > + .data = &sysctl_record_panic_msg,
> > + .maxlen = sizeof(int),
> > + .mode = 0644,
> > + .proc_handler = proc_dointvec_minmax,
> > + .extra1 = &zero,
> > + .extra2 = &one
> > + },
> > + {}
> > +};
> > +
> > +static struct ctl_table hv_root_table[] = {
> > + {
> > + .procname = "kernel",
> > + .mode = 0555,
> > + .child = hv_ctl_table
> > + },
> > + {}
> > +};
> >
> > /*
> > * vmbus_bus_init -Main vmbus driver initialization routine.
> > @@ -1065,6 +1136,38 @@ static int vmbus_bus_init(void)
> > * Only register if the crash MSRs are available
> > */
> > if (ms_hyperv.misc_features &
> > HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE) {
> > + u64 hyperv_crash_ctl;
> > + if (!hv_ctl_table_hdr) {
> When vmus_bus_init is invoked, would hv_ctl_table_hdr ever be
> Non-NULL?
> > + /*
> > + * Sysctl registration is not fatal, since default is
> > + * for operation.
> > + */
> > + hv_ctl_table_hdr =
> > + register_sysctl_table(hv_root_table);
> > + if (!hv_ctl_table_hdr)
> > + pr_err("Hyper-V: sysctl table register error");
> > + }
> > +
> > + /*
> > + * Register for panic kmsg callback only if the right
> > + * capability is supported by the hypervisor.
> > + */
> > + rdmsrl(HV_X64_MSR_CRASH_CTL, hyperv_crash_ctl);
> > + if (hyperv_crash_ctl &
> > HV_CRASH_CTL_CRASH_NOTIFY_MSG) {
> > + hv_panic_page = (void
> > *)get_zeroed_page(GFP_KERNEL);
> > + if (!hv_panic_page) {
> Why is this allocation failure fatal in terms failing the load of the driver?
> If we failed to allocate why can't we revert to the existing panic notification
> scheme.
We can. The idea was to force a diagnostic. If memory allocation is failing at driver
load, I am not sure how much further we will get. I will make it non-fatal in the next
version.
> > + ret = -ENOMEM;
> > + goto err_connect;
> > + }
> > +
> > + ret = kmsg_dump_register(&hv_kmsg_dumper);
> > + if (ret) {
> > + pr_err("Hyper-V: kmsg dump register error "
> > + "0x%x\n", ret);
> > + goto err_connect;
> > + }
> > + }
> > +
> > register_die_notifier(&hyperv_die_block);
> > atomic_notifier_chain_register(&panic_notifier_list,
> > &hyperv_panic_block);
> > @@ -1081,6 +1184,11 @@ static int vmbus_bus_init(void)
> > hv_remove_vmbus_irq();
> >
> > bus_unregister(&hv_bus);
> > + free_page((unsigned long)hv_panic_page);
> > + if (!hv_ctl_table_hdr) {
> > + unregister_sysctl_table(hv_ctl_table_hdr);
> > + hv_ctl_table_hdr = NULL;
> > + }
> >
> > return ret;
> > }
> > @@ -1785,10 +1893,18 @@ static void __exit vmbus_exit(void)
> > vmbus_free_channels();
> >
> > if (ms_hyperv.misc_features &
> > HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE) {
> > + kmsg_dump_unregister(&hv_kmsg_dumper);
> > unregister_die_notifier(&hyperv_die_block);
> > atomic_notifier_chain_unregister(&panic_notifier_list,
> > &hyperv_panic_block);
> > }
> > +
> > + free_page((unsigned long)hv_panic_page);
> > + if (!hv_ctl_table_hdr) {
> > + unregister_sysctl_table(hv_ctl_table_hdr);
> > + hv_ctl_table_hdr = NULL;
> > + }
> > +
> > bus_unregister(&hv_bus);
> >
> > cpuhp_remove_state(hyperv_cpuhp_online);
> > --
> > 2.7.4
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