>Subject: RE: [PATCH] Drivers: hv: move panic report code from vmbus to hv
>early init code
>
>From: longli@xxxxxxxxxxxxxxxxx <longli@xxxxxxxxxxxxxxxxx> Sent: Monday,
>April 10, 2023 7:10 PM
>>
>> The panic reporting code was added in commit 81b18bce48af
>> ("Drivers: HV: Send one page worth of kmsg dump over Hyper-V during
>> panic")
>>
>> It was added to the vmbus driver. The panic reporting has no
>> dependence on vmbus, and can be enabled at an earlier boot time when
>> Hyper-V is initialized.
>>
>> This patch moves the panic reporting code out of vmbus. There is no
>> functionality changes. During moving, also refactored some cleanup
>> functions into hv_kmsg_dump_unregister(), and removed unused function
>> hv_alloc_hyperv_page().
>>
>> Signed-off-by: Long Li <longli@xxxxxxxxxxxxx>
>> ---
>> drivers/hv/hv.c | 36 ------
>> drivers/hv/hv_common.c | 227
>+++++++++++++++++++++++++++++++++
>> drivers/hv/vmbus_drv.c | 186 ---------------------------
>> include/asm-generic/mshyperv.h | 1 -
>> 4 files changed, 227 insertions(+), 223 deletions(-)
>>
>> diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c index
>> 8b0dd8e5244d..88eca08c7030 100644
>> --- a/drivers/hv/hv.c
>> +++ b/drivers/hv/hv.c
>> @@ -38,42 +38,6 @@ int hv_init(void)
>> return 0;
>> }
>>
>> -/*
>> - * Functions for allocating and freeing memory with size and
>> - * alignment HV_HYP_PAGE_SIZE. These functions are needed because
>> - * the guest page size may not be the same as the Hyper-V page
>> - * size. We depend upon kmalloc() aligning power-of-two size
>> - * allocations to the allocation size boundary, so that the
>> - * allocated memory appears to Hyper-V as a page of the size
>> - * it expects.
>> - */
>> -
>> -void *hv_alloc_hyperv_page(void)
>> -{
>> - BUILD_BUG_ON(PAGE_SIZE < HV_HYP_PAGE_SIZE);
>> -
>> - if (PAGE_SIZE == HV_HYP_PAGE_SIZE)
>> - return (void *)__get_free_page(GFP_KERNEL);
>> - else
>> - return kmalloc(HV_HYP_PAGE_SIZE, GFP_KERNEL);
>> -}
>> -
>> -void *hv_alloc_hyperv_zeroed_page(void)
>> -{
>> - if (PAGE_SIZE == HV_HYP_PAGE_SIZE)
>> - return (void *)__get_free_page(GFP_KERNEL | __GFP_ZERO);
>> - else
>> - return kzalloc(HV_HYP_PAGE_SIZE, GFP_KERNEL);
>> -}
>> -
>> -void hv_free_hyperv_page(unsigned long addr) -{
>> - if (PAGE_SIZE == HV_HYP_PAGE_SIZE)
>> - free_page(addr);
>> - else
>> - kfree((void *)addr);
>> -}
>> -
>> /*
>> * hv_post_message - Post a message using the hypervisor message IPC.
>> *
>> diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c index
>> 52a6f89ccdbd..d696c2110349 100644
>> --- a/drivers/hv/hv_common.c
>> +++ b/drivers/hv/hv_common.c
>> @@ -17,8 +17,11 @@
>> #include <linux/export.h>
>> #include <linux/bitfield.h>
>> #include <linux/cpumask.h>
>> +#include <linux/sched/task_stack.h>
>> #include <linux/panic_notifier.h>
>> #include <linux/ptrace.h>
>> +#include <linux/kdebug.h>
>> +#include <linux/kmsg_dump.h>
>> #include <linux/slab.h>
>> #include <linux/dma-map-ops.h>
>> #include <asm/hyperv-tlfs.h>
>> @@ -54,6 +57,10 @@ EXPORT_SYMBOL_GPL(hyperv_pcpu_input_arg);
>> void * __percpu *hyperv_pcpu_output_arg;
>> EXPORT_SYMBOL_GPL(hyperv_pcpu_output_arg);
>>
>> +static void hv_kmsg_dump_unregister(void);
>> +
>> +static struct ctl_table_header *hv_ctl_table_hdr;
>> +
>> /*
>> * Hyper-V specific initialization and shutdown code that is
>> * common across all architectures. Called from architecture @@
>> -62,6 +69,12 @@ EXPORT_SYMBOL_GPL(hyperv_pcpu_output_arg);
>>
>> void __init hv_common_free(void)
>> {
>> + unregister_sysctl_table(hv_ctl_table_hdr);
>> + hv_ctl_table_hdr = NULL;
>> +
>> + if (ms_hyperv.misc_features &
>HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE)
>> + hv_kmsg_dump_unregister();
>> +
>> kfree(hv_vp_index);
>> hv_vp_index = NULL;
>>
>> @@ -72,6 +85,195 @@ void __init hv_common_free(void)
>> hyperv_pcpu_input_arg = NULL;
>> }
>>
>> +/*
>> + * Functions for allocating and freeing memory with size and
>> + * alignment HV_HYP_PAGE_SIZE. These functions are needed because
>> + * the guest page size may not be the same as the Hyper-V page
>> + * size. We depend upon kmalloc() aligning power-of-two size
>> + * allocations to the allocation size boundary, so that the
>> + * allocated memory appears to Hyper-V as a page of the size
>> + * it expects.
>> + */
>> +
>> +void *hv_alloc_hyperv_zeroed_page(void)
>> +{
>> + if (PAGE_SIZE == HV_HYP_PAGE_SIZE)
>> + return (void *)__get_free_page(GFP_KERNEL | __GFP_ZERO);
>> + else
>> + return kzalloc(HV_HYP_PAGE_SIZE, GFP_KERNEL); }
>> +EXPORT_SYMBOL_GPL(hv_alloc_hyperv_zeroed_page);
>> +
>> +void hv_free_hyperv_page(unsigned long addr) {
>> + if (PAGE_SIZE == HV_HYP_PAGE_SIZE)
>> + free_page(addr);
>> + else
>> + kfree((void *)addr);
>> +}
>> +EXPORT_SYMBOL_GPL(hv_free_hyperv_page);
>> +
>> +static void *hv_panic_page;
>> +static int sysctl_record_panic_msg = 1;
>> +
>> +static int hyperv_report_reg(void)
>> +{
>> + return !sysctl_record_panic_msg || !hv_panic_page; }
>
>Nit: The above function is used in only one place. The code could easily just go
>inline. Putting the code inline would probably be clearer anyway.
>
>> +
>> +static int hv_die_panic_notify_crash(struct notifier_block *self,
>> + unsigned long val, void *args);
>> +
>> +static struct notifier_block hyperv_die_report_block = {
>> + .notifier_call = hv_die_panic_notify_crash, };
>> +
>> +static struct notifier_block hyperv_panic_report_block = {
>> + .notifier_call = hv_die_panic_notify_crash, };
>> +
>> +/*
>> + * The following callback works both as die and panic notifier; its
>> + * goal is to provide panic information to the hypervisor unless the
>> + * kmsg dumper is used [see hv_kmsg_dump()], which provides more
>> + * information but isn't always available.
>> + *
>> + * Notice that both the panic/die report notifiers are registered
>> +only
>> + * if we have the capability HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE
>set.
>> + */
>> +static int hv_die_panic_notify_crash(struct notifier_block *self,
>> + unsigned long val, void *args) {
>> + struct pt_regs *regs;
>> + bool is_die;
>> +
>> + /* Don't notify Hyper-V unless we have a die oops event or panic. */
>> + if (self == &hyperv_panic_report_block) {
>> + is_die = false;
>> + regs = current_pt_regs();
>> + } else { /* die event */
>> + if (val != DIE_OOPS)
>> + return NOTIFY_DONE;
>> +
>> + is_die = true;
>> + regs = ((struct die_args *)args)->regs;
>> + }
>> +
>> + /*
>> + * Hyper-V should be notified only once about a panic/die. If we will
>> + * be calling hv_kmsg_dump() later with kmsg data, don't do the
>> + * notification here.
>> + */
>> + if (hyperv_report_reg())
>> + hyperv_report_panic(regs, val, is_die);
>> +
>> + return NOTIFY_DONE;
>> +}
>> +
>> +/*
>> + * 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)
>> +{
>> + struct kmsg_dump_iter iter;
>> + size_t bytes_written;
>> +
>> + /* We are only interested in panics. */
>> + if (reason != KMSG_DUMP_PANIC || !sysctl_record_panic_msg)
>> + return;
>> +
>> + /*
>> + * Write dump contents to the page. No need to synchronize; panic
>should
>> + * be single-threaded.
>> + */
>> + kmsg_dump_rewind(&iter);
>> + kmsg_dump_get_buffer(&iter, false, hv_panic_page,
>HV_HYP_PAGE_SIZE,
>> + &bytes_written);
>> + if (!bytes_written)
>> + return;
>> + /*
>> + * 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.
>> + */
>> + hv_set_register(HV_REGISTER_CRASH_P0, 0);
>> + hv_set_register(HV_REGISTER_CRASH_P1, 0);
>> + hv_set_register(HV_REGISTER_CRASH_P2, 0);
>> + hv_set_register(HV_REGISTER_CRASH_P3,
>virt_to_phys(hv_panic_page));
>> + hv_set_register(HV_REGISTER_CRASH_P4, bytes_written);
>> +
>> + /*
>> + * Let Hyper-V know there is crash data available along with
>> + * the panic message.
>> + */
>> + hv_set_register(HV_REGISTER_CRASH_CTL,
>> + (HV_CRASH_CTL_CRASH_NOTIFY |
>> + HV_CRASH_CTL_CRASH_NOTIFY_MSG));
>> +}
>> +
>> +static struct kmsg_dumper hv_kmsg_dumper = {
>> + .dump = hv_kmsg_dump,
>> +};
>> +
>> +static void hv_kmsg_dump_unregister(void) {
>> + kmsg_dump_unregister(&hv_kmsg_dumper);
>> + unregister_die_notifier(&hyperv_die_report_block);
>> + atomic_notifier_chain_unregister(&panic_notifier_list,
>> + &hyperv_panic_report_block);
>> +
>> + if (hv_panic_page) {
>
>No need to explicitly test for NULL. hv_free_hyperv_page() handles that case
>already.
>
>> + hv_free_hyperv_page((unsigned long)hv_panic_page);
>> + hv_panic_page = NULL;
>> + }
>> +}
>> +
>> +static void hv_kmsg_dump_register(void) {
>> + int ret;
>> +
>> + hv_panic_page = hv_alloc_hyperv_zeroed_page();
>> + if (!hv_panic_page) {
>> + pr_err("Hyper-V: panic message page memory allocation
>failed\n");
>> + return;
>> + }
>> +
>> + ret = kmsg_dump_register(&hv_kmsg_dumper);
>> + if (ret) {
>> + pr_err("Hyper-V: kmsg dump register error 0x%x\n", ret);
>> + hv_free_hyperv_page((unsigned long)hv_panic_page);
>> + hv_panic_page = NULL;
>> + }
>> +}
>> +
>> +/*
>> + * 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 = SYSCTL_ZERO,
>> + .extra2 = SYSCTL_ONE
>> + },
>> + {}
>> +};
>> +
>> +static struct ctl_table hv_root_table[] = {
>> + {
>> + .procname = "kernel",
>> + .mode = 0555,
>> + .child = hv_ctl_table
>> + },
>> + {}
>> +};
>> +
>> int __init hv_common_init(void)
>> {
>> int i;
>> @@ -84,8 +286,33 @@ int __init hv_common_init(void)
>> * kernel.
>> */
>> if (ms_hyperv.misc_features &
>HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE)
>> {
>> + u64 hyperv_crash_ctl;
>> +
>> crash_kexec_post_notifiers = true;
>> pr_info("Hyper-V: enabling crash_kexec_post_notifiers\n");
>> +
>> + /*
>> + * Panic message recording (sysctl_record_panic_msg)
>> + * is enabled by default in non-isolated guests and
>> + * disabled by default in isolated guests; the panic
>> + * message recording won't be available in isolated
>> + * guests should the following registration fail.
>> + */
>> + 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.
>> + */
>> + hyperv_crash_ctl = hv_get_register(HV_REGISTER_CRASH_CTL);
>> + if (hyperv_crash_ctl & HV_CRASH_CTL_CRASH_NOTIFY_MSG)
>> + hv_kmsg_dump_register();
>> +
>> + register_die_notifier(&hyperv_die_report_block);
>> + atomic_notifier_chain_register(&panic_notifier_list,
>> + &hyperv_panic_report_block);
>> }
>>
>> /*
>> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c index
>> d24dd65b33d4..96fb596ab68f 100644
>> --- a/drivers/hv/vmbus_drv.c
>> +++ b/drivers/hv/vmbus_drv.c
>> @@ -28,7 +28,6 @@
>> #include <linux/panic_notifier.h>
>> #include <linux/ptrace.h>
>> #include <linux/screen_info.h>
>> -#include <linux/kdebug.h>
>> #include <linux/efi.h>
>> #include <linux/random.h>
>> #include <linux/kernel.h>
>> @@ -63,11 +62,6 @@ int vmbus_interrupt;
>> */
>> static int sysctl_record_panic_msg = 1;
>>
>> -static int hyperv_report_reg(void)
>> -{
>> - return !sysctl_record_panic_msg || !hv_panic_page;
>> -}
>> -
>> /*
>> * The panic notifier below is responsible solely for unloading the
>> * vmbus connection, which is necessary in a panic event.
>> @@ -88,54 +82,6 @@ static struct notifier_block
>> hyperv_panic_vmbus_unload_block = {
>> .priority = INT_MIN + 1, /* almost the latest one to execute */
>> };
>>
>> -static int hv_die_panic_notify_crash(struct notifier_block *self,
>> - unsigned long val, void *args);
>> -
>> -static struct notifier_block hyperv_die_report_block = {
>> - .notifier_call = hv_die_panic_notify_crash,
>> -};
>> -static struct notifier_block hyperv_panic_report_block = {
>> - .notifier_call = hv_die_panic_notify_crash,
>> -};
>> -
>> -/*
>> - * The following callback works both as die and panic notifier; its
>> - * goal is to provide panic information to the hypervisor unless the
>> - * kmsg dumper is used [see hv_kmsg_dump()], which provides more
>> - * information but isn't always available.
>> - *
>> - * Notice that both the panic/die report notifiers are registered
>> only
>> - * if we have the capability HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE
>set.
>> - */
>> -static int hv_die_panic_notify_crash(struct notifier_block *self,
>> - unsigned long val, void *args)
>> -{
>> - struct pt_regs *regs;
>> - bool is_die;
>> -
>> - /* Don't notify Hyper-V unless we have a die oops event or panic. */
>> - if (self == &hyperv_panic_report_block) {
>> - is_die = false;
>> - regs = current_pt_regs();
>> - } else { /* die event */
>> - if (val != DIE_OOPS)
>> - return NOTIFY_DONE;
>> -
>> - is_die = true;
>> - regs = ((struct die_args *)args)->regs;
>> - }
>> -
>> - /*
>> - * Hyper-V should be notified only once about a panic/die. If we will
>> - * be calling hv_kmsg_dump() later with kmsg data, don't do the
>> - * notification here.
>> - */
>> - if (hyperv_report_reg())
>> - hyperv_report_panic(regs, val, is_die);
>> -
>> - return NOTIFY_DONE;
>> -}
>> -
>> static const char *fb_mmio_name = "fb_range"; static struct resource
>> *fb_mmio; static struct resource *hyperv_mmio; @@ -1377,98 +1323,6 @@
>> static irqreturn_t vmbus_percpu_isr(int irq, void *dev_id)
>> return IRQ_HANDLED;
>> }
>>
>> -/*
>> - * 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)
>> -{
>> - struct kmsg_dump_iter iter;
>> - size_t bytes_written;
>> -
>> - /* We are only interested in panics. */
>> - if ((reason != KMSG_DUMP_PANIC) || (!sysctl_record_panic_msg))
>> - return;
>> -
>> - /*
>> - * Write dump contents to the page. No need to synchronize; panic
>should
>> - * be single-threaded.
>> - */
>> - kmsg_dump_rewind(&iter);
>> - kmsg_dump_get_buffer(&iter, false, hv_panic_page,
>HV_HYP_PAGE_SIZE,
>> - &bytes_written);
>> - if (!bytes_written)
>> - return;
>> - /*
>> - * 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.
>> - */
>> - hv_set_register(HV_REGISTER_CRASH_P0, 0);
>> - hv_set_register(HV_REGISTER_CRASH_P1, 0);
>> - hv_set_register(HV_REGISTER_CRASH_P2, 0);
>> - hv_set_register(HV_REGISTER_CRASH_P3,
>virt_to_phys(hv_panic_page));
>> - hv_set_register(HV_REGISTER_CRASH_P4, bytes_written);
>> -
>> - /*
>> - * Let Hyper-V know there is crash data available along with
>> - * the panic message.
>> - */
>> - hv_set_register(HV_REGISTER_CRASH_CTL,
>> - (HV_CRASH_CTL_CRASH_NOTIFY |
>HV_CRASH_CTL_CRASH_NOTIFY_MSG));
>> -}
>> -
>> -static struct kmsg_dumper hv_kmsg_dumper = {
>> - .dump = hv_kmsg_dump,
>> -};
>> -
>> -static void hv_kmsg_dump_register(void) -{
>> - int ret;
>> -
>> - hv_panic_page = hv_alloc_hyperv_zeroed_page();
>> - if (!hv_panic_page) {
>> - pr_err("Hyper-V: panic message page memory allocation
>failed\n");
>> - return;
>> - }
>> -
>> - ret = kmsg_dump_register(&hv_kmsg_dumper);
>> - if (ret) {
>> - pr_err("Hyper-V: kmsg dump register error 0x%x\n", ret);
>> - hv_free_hyperv_page((unsigned long)hv_panic_page);
>> - hv_panic_page = NULL;
>> - }
>> -}
>> -
>> -static struct ctl_table_header *hv_ctl_table_hdr;
>> -
>> -/*
>> - * 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 = SYSCTL_ZERO,
>> - .extra2 = SYSCTL_ONE
>> - },
>> - {}
>> -};
>> -
>> -static struct ctl_table hv_root_table[] = {
>> - {
>> - .procname = "kernel",
>> - .mode = 0555,
>> - .child = hv_ctl_table
>> - },
>> - {}
>> -};
>> -
>> /*
>> * vmbus_bus_init -Main vmbus driver initialization routine.
>> *
>> @@ -1535,35 +1389,6 @@ static int vmbus_bus_init(void)
>> if (hv_is_isolation_supported())
>> sysctl_record_panic_msg = 0;
>
>The above two lines of code should move as well. Otherwise we have a
>window during early boot where the panic message might be dumped to the
>Hyper-V host in a CVM.
I'm sending v2 to address all the comments.
Thanks,
Long
