[PATCH v17 2/6] crash: add a new kexec flag for hotplug support
Sourabh Jain
sourabhjain at linux.ibm.com
Thu Feb 29 16:05:40 AEDT 2024
Hello Baoquan,
Do you have any comments or suggestions for this patch series,
especially for this patch?
Thanks,
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;
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