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authorEric DeVolder <eric.devolder@oracle.com>2023-08-15 00:44:44 +0300
committerAndrew Morton <akpm@linux-foundation.org>2023-08-25 02:25:14 +0300
commita72bbec70da285a7e09e53fb13c2da7da2032da9 (patch)
tree36a11085a5cf006f1f1090c6007094b3a137e49f /include/linux/kexec.h
parentea53ad9cf73b6b48608a69e626caeae87e5ddd11 (diff)
downloadlinux-a72bbec70da285a7e09e53fb13c2da7da2032da9.tar.xz
crash: hotplug support for kexec_load()
The hotplug support for kexec_load() requires changes to the userspace kexec-tools and a little extra help from the kernel. Given a kdump capture kernel loaded via kexec_load(), and a subsequent hotplug event, the crash hotplug handler finds the elfcorehdr and rewrites it to reflect the hotplug change. That is the desired outcome, however, at kernel panic time, the purgatory integrity check fails (because the elfcorehdr changed), and the capture kernel does not boot and no vmcore is generated. Therefore, the userspace kexec-tools/kexec must indicate to the kernel that the elfcorehdr can be modified (because the kexec excluded the elfcorehdr from the digest, and sized the elfcorehdr memory buffer appropriately). To facilitate hotplug support with kexec_load(): - a new kexec flag KEXEC_UPATE_ELFCOREHDR indicates that it is safe for the kernel to modify the kexec_load()'d elfcorehdr - the /sys/kernel/crash_elfcorehdr_size node communicates the preferred size of the elfcorehdr memory buffer - The sysfs crash_hotplug nodes (ie. /sys/devices/system/[cpu|memory]/crash_hotplug) dynamically take into account kexec_file_load() vs kexec_load() and KEXEC_UPDATE_ELFCOREHDR. This is critical so that the udev rule processing of crash_hotplug is all that is needed to determine if the userspace unload-then-load of the kdump image is to be skipped, or not. The proposed udev rule change looks like: # The kernel updates the crash elfcorehdr for CPU and memory changes SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" SUBSYSTEM=="memory", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" The table below indicates the behavior of kexec_load()'d kdump image updates (with the new udev crash_hotplug rule in place): Kernel |Kexec -------+-----+---- Old |Old |New | a | a -------+-----+---- New | a | b -------+-----+---- where kexec 'old' and 'new' delineate kexec-tools has the needed modifications for the crash hotplug feature, and kernel 'old' and 'new' delineate the kernel supports this crash hotplug feature. Behavior 'a' indicates the unload-then-reload of the entire kdump image. For the kexec 'old' column, the unload-then-reload occurs due to the missing flag KEXEC_UPDATE_ELFCOREHDR. An 'old' kernel (with 'new' kexec) does not present the crash_hotplug sysfs node, which leads to the unload-then-reload of the kdump image. Behavior 'b' indicates the desired optimized behavior of the kernel directly modifying the elfcorehdr and avoiding the unload-then-reload of the kdump image. If the udev rule is not updated with crash_hotplug node check, then no matter any combination of kernel or kexec is new or old, the kdump image continues to be unload-then-reload on hotplug changes. To fully support crash hotplug feature, there needs to be a rollout of kernel, kexec-tools and udev rule changes. However, the order of the rollout of these pieces does not matter; kexec_load()'d kdump images still function for hotplug as-is. Link: https://lkml.kernel.org/r/20230814214446.6659-7-eric.devolder@oracle.com Signed-off-by: Eric DeVolder <eric.devolder@oracle.com> Suggested-by: Hari Bathini <hbathini@linux.ibm.com> Acked-by: Hari Bathini <hbathini@linux.ibm.com> Acked-by: Baoquan He <bhe@redhat.com> Cc: Akhil Raj <lf32.dev@gmail.com> Cc: Bjorn Helgaas <bhelgaas@google.com> Cc: Borislav Petkov (AMD) <bp@alien8.de> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Dave Young <dyoung@redhat.com> Cc: David Hildenbrand <david@redhat.com> Cc: Eric W. Biederman <ebiederm@xmission.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Mimi Zohar <zohar@linux.ibm.com> Cc: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: "Rafael J. Wysocki" <rafael@kernel.org> Cc: Sean Christopherson <seanjc@google.com> Cc: Sourabh Jain <sourabhjain@linux.ibm.com> Cc: Takashi Iwai <tiwai@suse.de> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Thomas Weißschuh <linux@weissschuh.net> Cc: Valentin Schneider <vschneid@redhat.com> Cc: Vivek Goyal <vgoyal@redhat.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'include/linux/kexec.h')
-rw-r--r--include/linux/kexec.h14
1 files changed, 12 insertions, 2 deletions
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 172e9a544928..32c78078552c 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -320,6 +320,10 @@ struct kimage {
unsigned int preserve_context : 1;
/* 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;
+#endif
#ifdef ARCH_HAS_KIMAGE_ARCH
struct kimage_arch arch;
@@ -396,9 +400,9 @@ bool kexec_load_permitted(int kexec_image_type);
/* List of defined/legal kexec flags */
#ifndef CONFIG_KEXEC_JUMP
-#define KEXEC_FLAGS KEXEC_ON_CRASH
+#define KEXEC_FLAGS (KEXEC_ON_CRASH | KEXEC_UPDATE_ELFCOREHDR)
#else
-#define KEXEC_FLAGS (KEXEC_ON_CRASH | KEXEC_PRESERVE_CONTEXT)
+#define KEXEC_FLAGS (KEXEC_ON_CRASH | KEXEC_PRESERVE_CONTEXT | KEXEC_UPDATE_ELFCOREHDR)
#endif
/* List of defined/legal kexec file flags */
@@ -486,6 +490,8 @@ static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) {
static inline void arch_crash_handle_hotplug_event(struct kimage *image) { }
#endif
+int crash_check_update_elfcorehdr(void);
+
#ifndef crash_hotplug_cpu_support
static inline int crash_hotplug_cpu_support(void) { return 0; }
#endif
@@ -494,6 +500,10 @@ static inline int crash_hotplug_cpu_support(void) { return 0; }
static inline int crash_hotplug_memory_support(void) { return 0; }
#endif
+#ifndef crash_get_elfcorehdr_size
+static inline unsigned int crash_get_elfcorehdr_size(void) { return 0; }
+#endif
+
#else /* !CONFIG_KEXEC_CORE */
struct pt_regs;
struct task_struct;