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.
---
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 | 108 +++++++++++++++++++++++++++++++++++++
5 files changed, 150 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..16b0505 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
+ */
+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 +1136,30 @@ 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) {
+ if (!hv_ctl_table_hdr) {
+ /*
+ * 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");
+ }
+
+ hv_panic_page = (void *)get_zeroed_page(GFP_KERNEL);
+ if (!hv_panic_page) {
+ ret = -ENOMEM;
+ goto err_connect;
+ }
+
+ ret = kmsg_dump_register(&hv_kmsg_dumper);
+ if (ret) {
+ pr_err("Hyper-V - kmsg dump register failure 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 +1176,11 @@ 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 +1885,18 @@ 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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