[PATCH v17 2/6] crash: add a new kexec flag for hotplug support
Sourabh Jain
sourabhjain at linux.ibm.com
Mon Mar 4 15:46:07 AEDT 2024
Hello Hari,
On 02/03/24 18:47, Hari Bathini wrote:
>
>
> On 26/02/24 2:11 pm, 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.
>>
>
> Couple of minor nits. See comments below.
> Otherwise, looks good to me.
>
> Acked-by: Hari Bathini <hbathini at linux.ibm.com>
Thank you!
>
>> 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);
>> +}
>
> Introduction of the flag KEXEC_CRASH_HOTPLUG_SUPPORT warranted a bit
> of cleanup in x86 code. I think the changelog should call that out too.
Sure I will include it in v18.
>
>> 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.
>
> Also, this comment needs update as pointed out by Baoquan already.
Yes I will update it.
Thanks,
Sourabh
>> */
>> -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;
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