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From:   Long Li <longli@microsoft.com>
To:     "Michael Kelley (LINUX)" <mikelley@microsoft.com>,
        "longli@linuxonhyperv.com" <longli@linuxonhyperv.com>,
        KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
        Arnd Bergmann <arnd@arndb.de>
CC:     "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>
Subject: RE: [PATCH] Drivers: hv: move panic report code from vmbus to hv
 early init code
Thread-Topic: [PATCH] Drivers: hv: move panic report code from vmbus to hv
 early init code
Thread-Index: AQHZbBrIb0S6TsvepkeYbCWE5fxcFK8n/ocAgAHX1JA=
Date:   Thu, 13 Apr 2023 22:31:57 +0000
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References: <1681179010-17811-1-git-send-email-longli@linuxonhyperv.com>
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>Subject: RE: [PATCH] Drivers: hv: move panic report code from vmbus to hv
>early init code
>
>From: longli@linuxonhyperv.com <longli@linuxonhyperv.com> 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@microsoft.com>
>> ---
>>  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 =3D=3D 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 =3D=3D 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 =3D=3D 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 =3D NULL;
>> +
>> +	if (ms_hyperv.misc_features &
>HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE)
>> +		hv_kmsg_dump_unregister();
>> +
>>  	kfree(hv_vp_index);
>>  	hv_vp_index =3D NULL;
>>
>> @@ -72,6 +85,195 @@ void __init hv_common_free(void)
>>  	hyperv_pcpu_input_arg =3D 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 =3D=3D 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 =3D=3D 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 =3D 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 =3D {
>> +	.notifier_call =3D hv_die_panic_notify_crash, };
>> +
>> +static struct notifier_block hyperv_panic_report_block =3D {
>> +	.notifier_call =3D 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 =3D=3D &hyperv_panic_report_block) {
>> +		is_die =3D false;
>> +		regs =3D current_pt_regs();
>> +	} else { /* die event */
>> +		if (val !=3D DIE_OOPS)
>> +			return NOTIFY_DONE;
>> +
>> +		is_die =3D true;
>> +		regs =3D ((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 !=3D 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 =3D {
>> +	.dump =3D 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 c=
ase
>already.
>
>> +		hv_free_hyperv_page((unsigned long)hv_panic_page);
>> +		hv_panic_page =3D NULL;
>> +	}
>> +}
>> +
>> +static void hv_kmsg_dump_register(void) {
>> +	int ret;
>> +
>> +	hv_panic_page =3D hv_alloc_hyperv_zeroed_page();
>> +	if (!hv_panic_page) {
>> +		pr_err("Hyper-V: panic message page memory allocation
>failed\n");
>> +		return;
>> +	}
>> +
>> +	ret =3D 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 =3D 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[] =3D {
>> +	{
>> +		.procname	=3D "hyperv_record_panic_msg",
>> +		.data		=3D &sysctl_record_panic_msg,
>> +		.maxlen		=3D sizeof(int),
>> +		.mode		=3D 0644,
>> +		.proc_handler	=3D proc_dointvec_minmax,
>> +		.extra1		=3D SYSCTL_ZERO,
>> +		.extra2		=3D SYSCTL_ONE
>> +	},
>> +	{}
>> +};
>> +
>> +static struct ctl_table hv_root_table[] =3D {
>> +	{
>> +		.procname	=3D "kernel",
>> +		.mode		=3D 0555,
>> +		.child		=3D 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 =3D 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 =3D 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 =3D 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 =3D 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 =3D {
>>  	.priority	=3D 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 =3D {
>> -	.notifier_call =3D hv_die_panic_notify_crash,
>> -};
>> -static struct notifier_block hyperv_panic_report_block =3D {
>> -	.notifier_call =3D 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 =3D=3D &hyperv_panic_report_block) {
>> -		is_die =3D false;
>> -		regs =3D current_pt_regs();
>> -	} else { /* die event */
>> -		if (val !=3D DIE_OOPS)
>> -			return NOTIFY_DONE;
>> -
>> -		is_die =3D true;
>> -		regs =3D ((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 =3D "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 !=3D 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 =3D {
>> -	.dump =3D hv_kmsg_dump,
>> -};
>> -
>> -static void hv_kmsg_dump_register(void) -{
>> -	int ret;
>> -
>> -	hv_panic_page =3D hv_alloc_hyperv_zeroed_page();
>> -	if (!hv_panic_page) {
>> -		pr_err("Hyper-V: panic message page memory allocation
>failed\n");
>> -		return;
>> -	}
>> -
>> -	ret =3D 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 =3D 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[] =3D {
>> -	{
>> -		.procname       =3D "hyperv_record_panic_msg",
>> -		.data           =3D &sysctl_record_panic_msg,
>> -		.maxlen         =3D sizeof(int),
>> -		.mode           =3D 0644,
>> -		.proc_handler   =3D proc_dointvec_minmax,
>> -		.extra1		=3D SYSCTL_ZERO,
>> -		.extra2		=3D SYSCTL_ONE
>> -	},
>> -	{}
>> -};
>> -
>> -static struct ctl_table hv_root_table[] =3D {
>> -	{
>> -		.procname	=3D "kernel",
>> -		.mode		=3D 0555,
>> -		.child		=3D 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 =3D 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