Hello Eric,
On 14/06/22 04:12, Eric DeVolder wrote:
For x86_64, when CPU or memory is hot un/plugged, the crash
elfcorehdr, which describes the CPUs and memory in the system,
must also be updated.
When loading the crash kernel via kexec_load or kexec_file_load,
the elfcorehdr is identified at run time in
crash_core:handle_hotplug_event().
To update the elfcorehdr for x86_64, a new elfcorehdr must be
generated from the available CPUs and memory. The new elfcorehdr
is prepared into a buffer, and then installed over the top of
the existing elfcorehdr.
In the patch 'kexec: exclude elfcorehdr from the segment digest'
the need to update purgatory due to the change in elfcorehdr was
eliminated. As a result, no changes to purgatory or boot_params
(as the elfcorehdr= kernel command line parameter pointer
remains unchanged and correct) are needed, just elfcorehdr.
To accommodate a growing number of resources via hotplug, the
elfcorehdr segment must be sufficiently large enough to accommodate
changes, see the CRASH_MAX_MEMORY_RANGES configure item.
With this change, crash hotplug for kexec_file_load syscall
is supported. The kexec_load is also supported, but also
requires a corresponding change to userspace kexec-tools.
Signed-off-by: Eric DeVolder <eric.devolder@xxxxxxxxxx>
---
arch/x86/Kconfig | 11 ++++
arch/x86/kernel/crash.c | 116 ++++++++++++++++++++++++++++++++++++++++
2 files changed, 127 insertions(+)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 762a0b6ab8b6..e9eecff3b97d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2082,6 +2082,17 @@ config CRASH_DUMP
(CONFIG_RELOCATABLE=y).
For more details see Documentation/admin-guide/kdump/kdump.rst
+config CRASH_MAX_MEMORY_RANGES
+ depends on CRASH_DUMP && KEXEC_FILE && (HOTPLUG_CPU || MEMORY_HOTPLUG)
+ int
+ default 32768
+ help
+ For the kexec_file_load path, specify the maximum number of
+ memory regions, eg. as represented by the 'System RAM' entries
+ in /proc/iomem, that the elfcorehdr buffer/segment can accommodate.
+ This value is combined with NR_CPUS and multiplied by Elf64_Phdr
+ size to determine the final buffer size.
+
config KEXEC_JUMP
bool "kexec jump"
depends on KEXEC && HIBERNATION
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 9db41cce8d97..b9cdf7a0d868 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -25,6 +25,7 @@
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/memblock.h>
+#include <linux/highmem.h>
#include <asm/processor.h>
#include <asm/hardirq.h>
@@ -398,7 +399,17 @@ int crash_load_segments(struct kimage *image)
image->elf_headers = kbuf.buffer;
image->elf_headers_sz = kbuf.bufsz;
+#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
+ /* Ensure elfcorehdr segment large enough for hotplug changes */
+ kbuf.memsz = (CONFIG_NR_CPUS_DEFAULT + CONFIG_CRASH_MAX_MEMORY_RANGES) * sizeof(Elf64_Phdr);
+ /* For marking as usable to crash kernel */
+ image->elf_headers_sz = kbuf.memsz;
+ /* Record the index of the elfcorehdr segment */
+ image->elfcorehdr_index = image->nr_segments;
+ image->elfcorehdr_index_valid = true;
+#else
kbuf.memsz = kbuf.bufsz;
+#endif
kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
ret = kexec_add_buffer(&kbuf);
@@ -413,3 +424,108 @@ int crash_load_segments(struct kimage *image)
return ret;
}
#endif /* CONFIG_KEXEC_FILE */
+
+#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
+int crash_hotplug_support(void) { return 1; }
+void *arch_map_crash_pages(unsigned long paddr, unsigned long size)
+{
+ /*
+ * NOTE: The addresses and sizes passed to this routine have
+ * already been fully aligned on page boundaries. There is no
+ * need for massaging the address or size.
+ */
+ void *ptr = NULL;
+
+ /* NOTE: requires arch_kexec_[un]protect_crashkres() for write access */
+ if (size > 0) {
+ struct page *page = pfn_to_page(paddr >> PAGE_SHIFT);
+
+ ptr = kmap(page);
+ }
+
+ return ptr;
+}
+
+void arch_unmap_crash_pages(void **ptr)
+{
+ if (ptr) {
+ if (*ptr)
+ kunmap(*ptr);
+ *ptr = NULL;
+ }
+}
Aren't arch will have build issue if arch_[un]map_crash_pages methods
are not defined?
Thanks,
Sourabh Jain
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