RE: [PATCH] Drivers: hv: move panic report code from vmbus to hv early init code

[Michael Kelley (LINUX)]

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.

> 
> -	/*
> -	 * Only register if the crash MSRs are available
> -	 */
> -	if (ms_hyperv.misc_features & HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE) {
> -		u64 hyperv_crash_ctl;
> -		/*
> -		 * 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);
> -	}
> -
>  	/*
>  	 * Always register the vmbus unload panic notifier because we
>  	 * need to shut the VMbus channel connection on panic.
> @@ -1588,8 +1413,6 @@ static int vmbus_bus_init(void)
>  	}
>  err_setup:
>  	bus_unregister(&hv_bus);
> -	unregister_sysctl_table(hv_ctl_table_hdr);
> -	hv_ctl_table_hdr = NULL;
>  	return ret;
>  }
> 
> @@ -2818,13 +2641,6 @@ static void __exit vmbus_exit(void)
>  	vmbus_free_channels();
>  	kfree(vmbus_connection.channels);
> 
> -	if (ms_hyperv.misc_features & HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE) {
> -		kmsg_dump_unregister(&hv_kmsg_dumper);
> -		unregister_die_notifier(&hyperv_die_report_block);
> -		atomic_notifier_chain_unregister(&panic_notifier_list,
> -						&hyperv_panic_report_block);
> -	}
> -
>  	/*
>  	 * The vmbus panic notifier is always registered, hence we should
>  	 * also unconditionally unregister it here as well.
> @@ -2833,8 +2649,6 @@ static void __exit vmbus_exit(void)
>  					&hyperv_panic_vmbus_unload_block);
> 
>  	free_page((unsigned long)hv_panic_page);
> -	unregister_sysctl_table(hv_ctl_table_hdr);
> -	hv_ctl_table_hdr = NULL;
>  	bus_unregister(&hv_bus);
> 
>  	cpuhp_remove_state(hyperv_cpuhp_online);
> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
> index 8845a2eca339..df0dbccd719a 100644
> --- a/include/asm-generic/mshyperv.h
> +++ b/include/asm-generic/mshyperv.h
> @@ -186,7 +186,6 @@ void __init hv_common_free(void);
>  int hv_common_cpu_init(unsigned int cpu);
>  int hv_common_cpu_die(unsigned int cpu);
> 
> -void *hv_alloc_hyperv_page(void);
>  void *hv_alloc_hyperv_zeroed_page(void);
>  void hv_free_hyperv_page(unsigned long addr);
> 
> --
> 2.32.0