[PATCH v16 2/5] crash: add a new kexec flag for hotplug support
Baoquan He
bhe at redhat.com
Thu Feb 22 14:58:35 AEDT 2024
On 02/22/24 at 09:01am, Sourabh Jain wrote:
> Hello Baoquan,
>
> There are a lot of code movements introduced by your patch series, 'Split
> crash out from kexec and clean up related config items.'
>
> https://lore.kernel.org/all/20240221125752.36fbfe9c307496313198b60f@linux-foundation.org/
>
> Do you want me to rebase this patch series on top of the above patch series?
Yes, appreciate that, that would be very helpful. Rebasing this to
latest next/master. And I saw Hari's patch sereis, basically it's fine
to me. It will be great if this patch can sit on that patchset.
Thanks
Baoquan
>
> On 17/02/24 13:44, 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/kexec.h | 27 +++++++++++++++++----------
> > include/uapi/linux/kexec.h | 1 +
> > kernel/crash_core.c | 11 ++++-------
> > kernel/kexec.c | 4 ++--
> > kernel/kexec_file.c | 5 +++++
> > 9 files changed, 50 insertions(+), 41 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
> > index 9bb6607e864e..8be622e82ba8 100644
> > --- a/arch/x86/include/asm/kexec.h
> > +++ b/arch/x86/include/asm/kexec.h
> > @@ -211,15 +211,8 @@ 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 44744e9c68ec..7072aaee2ea0 100644
> > --- a/arch/x86/kernel/crash.c
> > +++ b/arch/x86/kernel/crash.c
> > @@ -398,20 +398,26 @@ 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 47de0f140ba6..24eb52607151 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 14f964a7719b..b80be8193970 100644
> > --- a/drivers/base/memory.c
> > +++ b/drivers/base/memory.c
> > @@ -514,7 +514,7 @@ 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/kexec.h b/include/linux/kexec.h
> > index 802052d9c64b..175152b99cb7 100644
> > --- a/include/linux/kexec.h
> > +++ b/include/linux/kexec.h
> > @@ -317,8 +317,10 @@ 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
> > @@ -396,9 +398,10 @@ 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 */
> > @@ -486,14 +489,18 @@ static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) {
> > 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 arch_crash_hotplug_support
> > +static inline int arch_crash_hotplug_support(struct kimage *image, unsigned long kexec_flags)
> > +{
> > -#ifndef crash_hotplug_memory_support
> > -static inline int crash_hotplug_memory_support(void) { return 0; }
> > +#ifdef CONFIG_KEXEC_FILE
> > + if (image->file_mode)
> > + return 1;
> > +#endif
> > + return kexec_flags & KEXEC_CRASH_HOTPLUG_SUPPORT;
> > +}
> > #endif
> > #ifndef crash_get_elfcorehdr_size
> > 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 b692ec5955de..3142884a5a5b 100644
> > --- a/kernel/crash_core.c
> > +++ b/kernel/crash_core.c
> > @@ -886,7 +886,7 @@ 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;
> > @@ -898,10 +898,7 @@ 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();
> > @@ -942,8 +939,8 @@ 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 8f35a5a42af8..9dc5b7ed5b73 100644
> > --- a/kernel/kexec.c
> > +++ b/kernel/kexec.c
> > @@ -130,8 +130,8 @@ 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 bef2f6f2571b..4dddf9264a69 100644
> > --- a/kernel/kexec_file.c
> > +++ b/kernel/kexec_file.c
> > @@ -373,6 +373,11 @@ 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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