[PATCH v17 2/6] crash: add a new kexec flag for hotplug support

[Sourabh Jain]

On 29/02/24 11:26, Baoquan He wrote:
> On 02/29/24 at 10:35am, Sourabh Jain wrote:
>> Hello Baoquan,
>>
>> Do you have any comments or suggestions for this patch series, especially
>> for this patch?
> Have applied this series and reviewing, will ack or add comment if any
> concern. Thanks.

Thanks, looking forward to your feedback!

- Sourabh

>
>> On 26/02/24 14:11, Sourabh Jain wrote:
>>> Commit a72bbec70da2 ("crash: hotplug support for kexec_load()")
>>> introduced a new kexec flag, `KEXEC_UPDATE_ELFCOREHDR`. Kexec tool uses
>>> this flag to indicate to the kernel that it is safe to modify the
>>> elfcorehdr of the kdump image loaded using the kexec_load system call.
>>>
>>> However, it is possible that architectures may need to update kexec
>>> segments other then elfcorehdr. For example, FDT (Flatten Device Tree)
>>> on PowerPC. Introducing a new kexec flag for every new kexec segment
>>> may not be a good solution. Hence, a generic kexec flag bit,
>>> `KEXEC_CRASH_HOTPLUG_SUPPORT`, is introduced to share the CPU/Memory
>>> hotplug support intent between the kexec tool and the kernel for the
>>> kexec_load system call.
>>>
>>> Now, if the kexec tool sends KEXEC_CRASH_HOTPLUG_SUPPORT kexec flag to
>>> the kernel, it indicates to the kernel that all the required kexec
>>> segment is skipped from SHA calculation and it is safe to update kdump
>>> image loaded using the kexec_load syscall.
>>>
>>> While loading the kdump image using the kexec_load syscall, the
>>> @update_elfcorehdr member of struct kimage is set if the kexec tool
>>> sends the KEXEC_UPDATE_ELFCOREHDR kexec flag. This member is later used
>>> to determine whether it is safe to update elfcorehdr on hotplug events.
>>> However, with the introduction of the KEXEC_CRASH_HOTPLUG_SUPPORT kexec
>>> flag, the kexec tool could mark all the required kexec segments on an
>>> architecture as safe to update. So rename the @update_elfcorehdr to
>>> @hotplug_support. If @hotplug_support is set, the kernel can safely
>>> update all the required kexec segments of the kdump image during
>>> CPU/Memory hotplug events.
>>>
>>> Introduce an architecture-specific function to process kexec flags for
>>> determining hotplug support. Set the @hotplug_support member of struct
>>> kimage for both kexec_load and kexec_file_load system calls. This
>>> simplifies kernel checks to identify hotplug support for the currently
>>> loaded kdump image by just examining the value of @hotplug_support.
>>>
>>> Signed-off-by: Sourabh Jain <sourabhjain at linux.ibm.com>
>>> Cc: Akhil Raj <lf32.dev at gmail.com>
>>> Cc: Andrew Morton <akpm at linux-foundation.org>
>>> Cc: Aneesh Kumar K.V <aneesh.kumar at kernel.org>
>>> Cc: Baoquan He <bhe at redhat.com>
>>> Cc: Borislav Petkov (AMD) <bp at alien8.de>
>>> Cc: Boris Ostrovsky <boris.ostrovsky at oracle.com>
>>> Cc: Christophe Leroy <christophe.leroy at csgroup.eu>
>>> Cc: Dave Hansen <dave.hansen at linux.intel.com>
>>> Cc: Dave Young <dyoung at redhat.com>
>>> Cc: David Hildenbrand <david at redhat.com>
>>> Cc: Eric DeVolder <eric.devolder at oracle.com>
>>> Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
>>> Cc: Hari Bathini <hbathini at linux.ibm.com>
>>> Cc: Laurent Dufour <laurent.dufour at fr.ibm.com>
>>> Cc: Mahesh Salgaonkar <mahesh at linux.ibm.com>
>>> Cc: Michael Ellerman <mpe at ellerman.id.au>
>>> Cc: Mimi Zohar <zohar at linux.ibm.com>
>>> Cc: Naveen N Rao <naveen at kernel.org>
>>> Cc: Oscar Salvador <osalvador at suse.de>
>>> Cc: Thomas Gleixner <tglx at linutronix.de>
>>> Cc: Valentin Schneider <vschneid at redhat.com>
>>> Cc: Vivek Goyal <vgoyal at redhat.com>
>>> Cc: kexec at lists.infradead.org
>>> Cc: x86 at kernel.org
>>> ---
>>>    arch/x86/include/asm/kexec.h | 11 ++---------
>>>    arch/x86/kernel/crash.c      | 28 +++++++++++++++++-----------
>>>    drivers/base/cpu.c           |  2 +-
>>>    drivers/base/memory.c        |  2 +-
>>>    include/linux/crash_core.h   | 13 ++++++-------
>>>    include/linux/kexec.h        | 11 +++++++----
>>>    include/uapi/linux/kexec.h   |  1 +
>>>    kernel/crash_core.c          | 11 ++++-------
>>>    kernel/kexec.c               |  4 ++--
>>>    kernel/kexec_file.c          |  5 +++++
>>>    10 files changed, 46 insertions(+), 42 deletions(-)
>>>
>>> diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
>>> index cb1320ebbc23..ae5482a2f0ca 100644
>>> --- a/arch/x86/include/asm/kexec.h
>>> +++ b/arch/x86/include/asm/kexec.h
>>> @@ -210,15 +210,8 @@ extern void kdump_nmi_shootdown_cpus(void);
>>>    void arch_crash_handle_hotplug_event(struct kimage *image, void *arg);
>>>    #define arch_crash_handle_hotplug_event arch_crash_handle_hotplug_event
>>> -#ifdef CONFIG_HOTPLUG_CPU
>>> -int arch_crash_hotplug_cpu_support(void);
>>> -#define crash_hotplug_cpu_support arch_crash_hotplug_cpu_support
>>> -#endif
>>> -
>>> -#ifdef CONFIG_MEMORY_HOTPLUG
>>> -int arch_crash_hotplug_memory_support(void);
>>> -#define crash_hotplug_memory_support arch_crash_hotplug_memory_support
>>> -#endif
>>> +int arch_crash_hotplug_support(struct kimage *image, unsigned long kexec_flags);
>>> +#define arch_crash_hotplug_support arch_crash_hotplug_support
>>>    unsigned int arch_crash_get_elfcorehdr_size(void);
>>>    #define crash_get_elfcorehdr_size arch_crash_get_elfcorehdr_size
>>> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
>>> index 2a682fe86352..f06501445cd9 100644
>>> --- a/arch/x86/kernel/crash.c
>>> +++ b/arch/x86/kernel/crash.c
>>> @@ -402,20 +402,26 @@ int crash_load_segments(struct kimage *image)
>>>    #undef pr_fmt
>>>    #define pr_fmt(fmt) "crash hp: " fmt
>>> -/* These functions provide the value for the sysfs crash_hotplug nodes */
>>> -#ifdef CONFIG_HOTPLUG_CPU
>>> -int arch_crash_hotplug_cpu_support(void)
>>> +int arch_crash_hotplug_support(struct kimage *image, unsigned long kexec_flags)
>>>    {
>>> -	return crash_check_update_elfcorehdr();
>>> -}
>>> -#endif
>>> -#ifdef CONFIG_MEMORY_HOTPLUG
>>> -int arch_crash_hotplug_memory_support(void)
>>> -{
>>> -	return crash_check_update_elfcorehdr();
>>> -}
>>> +#ifdef CONFIG_KEXEC_FILE
>>> +	if (image->file_mode)
>>> +		return 1;
>>>    #endif
>>> +	/*
>>> +	 * Initially, crash hotplug support for kexec_load was added
>>> +	 * with the KEXEC_UPDATE_ELFCOREHDR flag. Later, this
>>> +	 * functionality was expanded to accommodate multiple kexec
>>> +	 * segment updates, leading to the introduction of the
>>> +	 * KEXEC_CRASH_HOTPLUG_SUPPORT kexec flag bit. Consequently,
>>> +	 * when the kexec tool sends either of these flags, it indicates
>>> +	 * that the required kexec segment (elfcorehdr) is excluded from
>>> +	 * the SHA calculation.
>>> +	 */
>>> +	return (kexec_flags & KEXEC_UPDATE_ELFCOREHDR ||
>>> +		kexec_flags & KEXEC_CRASH_HOTPLUG_SUPPORT);
>>> +}
>>>    unsigned int arch_crash_get_elfcorehdr_size(void)
>>>    {
>>> diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
>>> index 5ae1496ccc06..a23489b8c8f0 100644
>>> --- a/drivers/base/cpu.c
>>> +++ b/drivers/base/cpu.c
>>> @@ -306,7 +306,7 @@ static ssize_t crash_hotplug_show(struct device *dev,
>>>    				     struct device_attribute *attr,
>>>    				     char *buf)
>>>    {
>>> -	return sysfs_emit(buf, "%d\n", crash_hotplug_cpu_support());
>>> +	return sysfs_emit(buf, "%d\n", crash_check_hotplug_support());
>>>    }
>>>    static DEVICE_ATTR_ADMIN_RO(crash_hotplug);
>>>    #endif
>>> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
>>> index c0436f46cfb7..67858eeb92ed 100644
>>> --- a/drivers/base/memory.c
>>> +++ b/drivers/base/memory.c
>>> @@ -535,7 +535,7 @@ static DEVICE_ATTR_RW(auto_online_blocks);
>>>    static ssize_t crash_hotplug_show(struct device *dev,
>>>    				       struct device_attribute *attr, char *buf)
>>>    {
>>> -	return sysfs_emit(buf, "%d\n", crash_hotplug_memory_support());
>>> +	return sysfs_emit(buf, "%d\n", crash_check_hotplug_support());
>>>    }
>>>    static DEVICE_ATTR_RO(crash_hotplug);
>>>    #endif
>>> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
>>> index 647e928efee8..44305336314e 100644
>>> --- a/include/linux/crash_core.h
>>> +++ b/include/linux/crash_core.h
>>> @@ -40,14 +40,13 @@ static inline void arch_kexec_unprotect_crashkres(void) { }
>>>    static inline void arch_crash_handle_hotplug_event(struct kimage *image, void *arg) { }
>>>    #endif
>>> -int crash_check_update_elfcorehdr(void);
>>> +int crash_check_hotplug_support(void);
>>> -#ifndef crash_hotplug_cpu_support
>>> -static inline int crash_hotplug_cpu_support(void) { return 0; }
>>> -#endif
>>> -
>>> -#ifndef crash_hotplug_memory_support
>>> -static inline int crash_hotplug_memory_support(void) { return 0; }
>>> +#ifndef arch_crash_hotplug_support
>>> +static inline int arch_crash_hotplug_support(struct kimage *image, unsigned long kexec_flags)
>>> +{
>>> +	return 0;
>>> +}
>>>    #endif
>>>    #ifndef crash_get_elfcorehdr_size
>>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
>>> index 060835bb82d5..5b93a5767413 100644
>>> --- a/include/linux/kexec.h
>>> +++ b/include/linux/kexec.h
>>> @@ -319,8 +319,10 @@ struct kimage {
>>>    	/* If set, we are using file mode kexec syscall */
>>>    	unsigned int file_mode:1;
>>>    #ifdef CONFIG_CRASH_HOTPLUG
>>> -	/* If set, allow changes to elfcorehdr of kexec_load'd image */
>>> -	unsigned int update_elfcorehdr:1;
>>> +	/* If set, it is safe to update kexec segments that are
>>> +	 * excluded from SHA calculation.
>>> +	 */
>>> +	unsigned int hotplug_support:1;
>>>    #endif
>>>    #ifdef ARCH_HAS_KIMAGE_ARCH
>>> @@ -391,9 +393,10 @@ bool kexec_load_permitted(int kexec_image_type);
>>>    /* List of defined/legal kexec flags */
>>>    #ifndef CONFIG_KEXEC_JUMP
>>> -#define KEXEC_FLAGS    (KEXEC_ON_CRASH | KEXEC_UPDATE_ELFCOREHDR)
>>> +#define KEXEC_FLAGS    (KEXEC_ON_CRASH | KEXEC_UPDATE_ELFCOREHDR | KEXEC_CRASH_HOTPLUG_SUPPORT)
>>>    #else
>>> -#define KEXEC_FLAGS    (KEXEC_ON_CRASH | KEXEC_PRESERVE_CONTEXT | KEXEC_UPDATE_ELFCOREHDR)
>>> +#define KEXEC_FLAGS    (KEXEC_ON_CRASH | KEXEC_PRESERVE_CONTEXT | KEXEC_UPDATE_ELFCOREHDR | \
>>> +			KEXEC_CRASH_HOTPLUG_SUPPORT)
>>>    #endif
>>>    /* List of defined/legal kexec file flags */
>>> diff --git a/include/uapi/linux/kexec.h b/include/uapi/linux/kexec.h
>>> index c17bb096ea68..5ae1741ea8ea 100644
>>> --- a/include/uapi/linux/kexec.h
>>> +++ b/include/uapi/linux/kexec.h
>>> @@ -13,6 +13,7 @@
>>>    #define KEXEC_ON_CRASH		0x00000001
>>>    #define KEXEC_PRESERVE_CONTEXT	0x00000002
>>>    #define KEXEC_UPDATE_ELFCOREHDR	0x00000004
>>> +#define KEXEC_CRASH_HOTPLUG_SUPPORT 0x00000008
>>>    #define KEXEC_ARCH_MASK		0xffff0000
>>>    /*
>>> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
>>> index 70fa8111a9d6..630c4fd7ea39 100644
>>> --- a/kernel/crash_core.c
>>> +++ b/kernel/crash_core.c
>>> @@ -496,7 +496,7 @@ static DEFINE_MUTEX(__crash_hotplug_lock);
>>>     * It reflects the kernel's ability/permission to update the crash
>>>     * elfcorehdr directly.
>>>     */
>>> -int crash_check_update_elfcorehdr(void)
>>> +int crash_check_hotplug_support(void)
>>>    {
>>>    	int rc = 0;
>>> @@ -508,10 +508,7 @@ int crash_check_update_elfcorehdr(void)
>>>    		return 0;
>>>    	}
>>>    	if (kexec_crash_image) {
>>> -		if (kexec_crash_image->file_mode)
>>> -			rc = 1;
>>> -		else
>>> -			rc = kexec_crash_image->update_elfcorehdr;
>>> +		rc = kexec_crash_image->hotplug_support;
>>>    	}
>>>    	/* Release lock now that update complete */
>>>    	kexec_unlock();
>>> @@ -552,8 +549,8 @@ static void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu,
>>>    	image = kexec_crash_image;
>>> -	/* Check that updating elfcorehdr is permitted */
>>> -	if (!(image->file_mode || image->update_elfcorehdr))
>>> +	/* Check that kexec segments update is permitted */
>>> +	if (!image->hotplug_support)
>>>    		goto out;
>>>    	if (hp_action == KEXEC_CRASH_HP_ADD_CPU ||
>>> diff --git a/kernel/kexec.c b/kernel/kexec.c
>>> index bab542fc1463..a6b3f96bb50c 100644
>>> --- a/kernel/kexec.c
>>> +++ b/kernel/kexec.c
>>> @@ -135,8 +135,8 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
>>>    		image->preserve_context = 1;
>>>    #ifdef CONFIG_CRASH_HOTPLUG
>>> -	if (flags & KEXEC_UPDATE_ELFCOREHDR)
>>> -		image->update_elfcorehdr = 1;
>>> +	if ((flags & KEXEC_ON_CRASH) && arch_crash_hotplug_support(image, flags))
>>> +		image->hotplug_support = 1;
>>>    #endif
>>>    	ret = machine_kexec_prepare(image);
>>> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
>>> index 2d1db05fbf04..3d64290d24c9 100644
>>> --- a/kernel/kexec_file.c
>>> +++ b/kernel/kexec_file.c
>>> @@ -376,6 +376,11 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
>>>    	if (ret)
>>>    		goto out;
>>> +#ifdef CONFIG_CRASH_HOTPLUG
>>> +	if ((flags & KEXEC_FILE_ON_CRASH) && arch_crash_hotplug_support(image, flags))
>>> +		image->hotplug_support = 1;
>>> +#endif
>>> +
>>>    	ret = machine_kexec_prepare(image);
>>>    	if (ret)
>>>    		goto out;