Re: [PATCH v16 2/5] crash: add a new kexec flag for hotplug support

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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@xxxxxxxxxxxxxxxxxxxx/
> 
> 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@xxxxxxxxxxxxx>
> > Cc: Akhil Raj <lf32.dev@xxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxx>
> > Cc: Baoquan He <bhe@xxxxxxxxxx>
> > Cc: Borislav Petkov (AMD) <bp@xxxxxxxxx>
> > Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> > Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> > Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> > Cc: Dave Young <dyoung@xxxxxxxxxx>
> > Cc: David Hildenbrand <david@xxxxxxxxxx>
> > Cc: Eric DeVolder <eric.devolder@xxxxxxxxxx>
> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Cc: Hari Bathini <hbathini@xxxxxxxxxxxxx>
> > Cc: Laurent Dufour <laurent.dufour@xxxxxxxxxx>
> > Cc: Mahesh Salgaonkar <mahesh@xxxxxxxxxxxxx>
> > Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> > Cc: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> > Cc: Naveen N Rao <naveen@xxxxxxxxxx>
> > Cc: Oscar Salvador <osalvador@xxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
> > Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
> > Cc: kexec@xxxxxxxxxxxxxxxxxxx
> > Cc: x86@xxxxxxxxxx
> > ---
> >   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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