[PATCH v13 2/6] crash: make CPU and Memory hotplug support reporting flexible

Sourabh Jain sourabhjain at linux.ibm.com
Mon Dec 4 16:32:49 AEDT 2023

Architectures' specific functions `arch_crash_hotplug_cpu_support()` and
`arch_crash_hotplug_memory_support()` advertise the kernel's capability
to update the kdump image on CPU and Memory hotplug events to userspace
via the sysfs interface. These architecture-specific functions need to
access various attributes of the `kexec_crash_image` object to determine
whether the kernel can update the kdump image and advertise this
information to userspace accordingly.

As the architecture-specific code is not exposed to the APIs required to
acquire the lock for accessing the `kexec_crash_image` object, it calls
a generic function, `crash_check_update_elfcorehdr()`, to determine
whether the kernel can update the kdump image or not.

The lack of access to the `kexec_crash_image` object in
architecture-specific code restricts architectures from performing
additional architecture-specific checks required to determine if the
kdump image is updatable or not. For instance, on PowerPC, the kernel
can update the kdump image only if both the elfcorehdr and FDT are
marked as updatable for the `kexec_load` system call.

So define two generic functions, `crash_hotplug_cpu_support()` and
`crash_hotplug_memory_support()`, which are called when userspace
attempts to read the crash CPU and Memory hotplug support via the sysfs
interface. These functions take the necessary locks needed to access the
`kexec_crash_image` object and then forward it to the
architecture-specific handler to do the rest.

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: 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: 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 |  8 ++++----
 arch/x86/kernel/crash.c      | 20 +++++++++++++++-----
 include/linux/kexec.h        | 13 +++++++------
 kernel/crash_core.c          | 23 +++++++++++++++++------
 4 files changed, 43 insertions(+), 21 deletions(-)

diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
index 9bb6607e864e..5c88d27b086d 100644
--- a/arch/x86/include/asm/kexec.h
+++ b/arch/x86/include/asm/kexec.h
@@ -212,13 +212,13 @@ void arch_crash_handle_hotplug_event(struct kimage *image, void *arg);
 #define arch_crash_handle_hotplug_event arch_crash_handle_hotplug_event
-int arch_crash_hotplug_cpu_support(void);
-#define crash_hotplug_cpu_support arch_crash_hotplug_cpu_support
+int arch_crash_hotplug_cpu_support(struct kimage *image);
+#define arch_crash_hotplug_cpu_support arch_crash_hotplug_cpu_support
-int arch_crash_hotplug_memory_support(void);
-#define crash_hotplug_memory_support arch_crash_hotplug_memory_support
+int arch_crash_hotplug_memory_support(struct kimage *image);
+#define arch_crash_hotplug_memory_support arch_crash_hotplug_memory_support
 unsigned int arch_crash_get_elfcorehdr_size(void);
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 0d7b2657beb6..ad5941665589 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -398,18 +398,28 @@ 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 */
+static int crash_hotplug_support(struct kimage *image)
+	if (image->file_mode)
+		return 1;
+	return image->update_elfcorehdr;
-int arch_crash_hotplug_cpu_support(void)
+/* These functions provide the value for the sysfs crash_hotplug nodes */
+int arch_crash_hotplug_cpu_support(struct kimage *image)
-	return crash_check_update_elfcorehdr();
+	return crash_hotplug_support(image);
-int arch_crash_hotplug_memory_support(void)
+int arch_crash_hotplug_memory_support(struct kimage *image)
-	return crash_check_update_elfcorehdr();
+	return crash_hotplug_support(image);
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index ee28c09a7fb0..0f6ea35879ee 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -486,16 +486,17 @@ 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) { }
-int crash_check_update_elfcorehdr(void);
-#ifndef crash_hotplug_cpu_support
-static inline int crash_hotplug_cpu_support(void) { return 0; }
+#ifndef arch_crash_hotplug_cpu_support
+static inline int arch_crash_hotplug_cpu_support(struct kimage *image) { return 0; }
-#ifndef crash_hotplug_memory_support
-static inline int crash_hotplug_memory_support(void) { return 0; }
+#ifndef arch_crash_hotplug_memory_support
+static inline int arch_crash_hotplug_memory_support(struct kimage *image) { return 0; }
+extern int crash_hotplug_cpu_support(void);
+extern int crash_hotplug_memory_support(void);
 #ifndef crash_get_elfcorehdr_size
 static inline unsigned int crash_get_elfcorehdr_size(void) { return 0; }
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index b9190265fe52..b621f03c1104 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -892,12 +892,14 @@ DEFINE_MUTEX(__crash_hotplug_lock);
 #define crash_hotplug_lock() mutex_lock(&__crash_hotplug_lock)
 #define crash_hotplug_unlock() mutex_unlock(&__crash_hotplug_lock)
+#define CPU_HOTPLUG	0
+#define MEM_HOTPLUG	1
  * This routine utilized when the crash_hotplug sysfs node is read.
  * It reflects the kernel's ability/permission to update the crash
  * elfcorehdr directly.
-int crash_check_update_elfcorehdr(void)
+static int crash_hotplug_support(int hotplug)
 	int rc = 0;
@@ -909,18 +911,27 @@ 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;
+		if (hotplug == CPU_HOTPLUG)
+			rc = arch_crash_hotplug_cpu_support(kexec_crash_image);
+		else if (hotplug == MEM_HOTPLUG)
+			rc = arch_crash_hotplug_memory_support(kexec_crash_image);
 	/* Release lock now that update complete */
 	return rc;
+int crash_hotplug_cpu_support(void)
+	return crash_hotplug_support(CPU_HOTPLUG);
+int crash_hotplug_memory_support(void)
+	return crash_hotplug_support(MEM_HOTPLUG);
  * To accurately reflect hot un/plug changes of cpu and memory resources
  * (including onling and offlining of those resources), the elfcorehdr

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