When CPU or memory is hot un/plugged, the crash elfcorehdr, which
describes the CPUs and memory in the system, must also be updated.
A new elfcorehdr is generated from the available CPUs and memory
into a buffer, and then installed over the top of the existing
elfcorehdr. The segment containing the elfcorehdr is identified
at run time in crash_core:handle_hotplug_event(), which works for
both the kexec_load() and kexec_file_load() syscalls.
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 description.
Signed-off-by: Eric DeVolder <[email protected]>
---
arch/x86/Kconfig | 12 ++++
arch/x86/include/asm/kexec.h | 15 +++++
arch/x86/kernel/crash.c | 112 ++++++++++++++++++++++++++++++++++-
3 files changed, 136 insertions(+), 3 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 3604074a878b..09e9b7a091ed 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2119,6 +2119,18 @@ config CRASH_DUMP
(CONFIG_RELOCATABLE=y).
For more details see Documentation/admin-guide/kdump/kdump.rst
+config CRASH_HOTPLUG
+ bool "Update the crash elfcorehdr on system configuration changes"
+ default n
+ depends on CRASH_DUMP && (HOTPLUG_CPU || MEMORY_HOTPLUG)
+ help
+ Enable direct update to the crash elfcorehdr (which contains
+ the list of CPUs and memory regions to be dumped upon a crash)
+ in response to hot plug/unplug of CPUs or memory. This is a much
+ more advanced approach than userspace attempting that.
+
+ If unsure, say Y.
+
config KEXEC_JUMP
bool "kexec jump"
depends on KEXEC && HIBERNATION
diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
index a3760ca796aa..1bc852ce347d 100644
--- a/arch/x86/include/asm/kexec.h
+++ b/arch/x86/include/asm/kexec.h
@@ -212,6 +212,21 @@ typedef void crash_vmclear_fn(void);
extern crash_vmclear_fn __rcu *crash_vmclear_loaded_vmcss;
extern void kdump_nmi_shootdown_cpus(void);
+#ifdef CONFIG_CRASH_HOTPLUG
+void arch_crash_handle_hotplug_event(struct kimage *image);
+#define arch_crash_handle_hotplug_event arch_crash_handle_hotplug_event
+
+#ifdef CONFIG_HOTPLUG_CPU
+static inline int crash_hotplug_cpu_support(void) { return 1; }
+#define crash_hotplug_cpu_support crash_hotplug_cpu_support
+#endif
+
+#ifdef CONFIG_MEMORY_HOTPLUG
+static inline int crash_hotplug_memory_support(void) { return 1; }
+#define crash_hotplug_memory_support crash_hotplug_memory_support
+#endif
+#endif
+
#endif /* __ASSEMBLY__ */
#endif /* _ASM_X86_KEXEC_H */
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 9ceb93c176a6..76e2431dec63 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -42,6 +42,21 @@
#include <asm/crash.h>
#include <asm/cmdline.h>
+/*
+ * For the kexec_file_load() syscall path, specify the maximum number of
+ * memory regions that the elfcorehdr buffer/segment can accommodate.
+ * These regions are obtained via walk_system_ram_res(); eg. the
+ * 'System RAM' entries in /proc/iomem.
+ * This value is combined with NR_CPUS_DEFAULT and multiplied by
+ * sizeof(Elf64_Phdr) to determine the final elfcorehdr memory buffer/
+ * segment size.
+ * The value 8192, for example, covers a (sparsely populated) 1TiB system
+ * consisting of 128MiB memblocks, while resulting in an elfcorehdr
+ * memory buffer/segment size under 1MiB. This represents a sane choice
+ * to accommodate both baremetal and virtual machine configurations.
+ */
+#define CRASH_MAX_MEMORY_RANGES 8192
+
/* Used while preparing memory map entries for second kernel */
struct crash_memmap_data {
struct boot_params *params;
@@ -394,10 +409,37 @@ int crash_load_segments(struct kimage *image)
if (ret)
return ret;
- image->elf_headers = kbuf.buffer;
- image->elf_headers_sz = kbuf.bufsz;
+ image->elf_headers = kbuf.buffer;
+ image->elf_headers_sz = kbuf.bufsz;
+ kbuf.memsz = kbuf.bufsz;
+
+ if (IS_ENABLED(CONFIG_CRASH_HOTPLUG)) {
+ /*
+ * Ensure the elfcorehdr segment large enough for hotplug changes.
+ * Start with VMCOREINFO and kernel_map.
+ */
+ unsigned long pnum = 2;
+
+ if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
+ pnum += CONFIG_NR_CPUS_DEFAULT;
+
+ if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
+ pnum += CRASH_MAX_MEMORY_RANGES;
+
+ if (pnum < (unsigned long)PN_XNUM) {
+ kbuf.memsz = pnum * sizeof(Elf64_Phdr);
+ kbuf.memsz += sizeof(Elf64_Ehdr);
+
+ image->elfcorehdr_index = image->nr_segments;
+ image->elfcorehdr_index_valid = true;
+
+ /* Mark as usable to crash kernel, else crash kernel fails on boot */
+ image->elf_headers_sz = kbuf.memsz;
+ } else {
+ pr_err("number of Phdrs %lu exceeds max\n", pnum);
+ }
+ }
- kbuf.memsz = kbuf.bufsz;
kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
ret = kexec_add_buffer(&kbuf);
@@ -412,3 +454,67 @@ int crash_load_segments(struct kimage *image)
return ret;
}
#endif /* CONFIG_KEXEC_FILE */
+
+#ifdef CONFIG_CRASH_HOTPLUG
+
+#undef pr_fmt
+#define pr_fmt(fmt) "crash hp: " fmt
+
+/**
+ * arch_crash_handle_hotplug_event() - Handle hotplug elfcorehdr changes
+ * @image: the active struct kimage
+ *
+ * To accurately reflect hot un/plug changes, the new elfcorehdr
+ * is prepared in a kernel buffer, and then it is written on top
+ * of the existing/old elfcorehdr.
+ */
+void arch_crash_handle_hotplug_event(struct kimage *image)
+{
+ void *elfbuf = NULL, *old_elfcorehdr;
+ unsigned long mem, memsz;
+ unsigned long elfsz = 0;
+
+ /*
+ * Create the new elfcorehdr reflecting the changes to CPU and/or
+ * memory resources.
+ */
+ if (prepare_elf_headers(image, &elfbuf, &elfsz)) {
+ pr_err("unable to prepare elfcore headers");
+ goto out;
+ }
+
+ /*
+ * Obtain address and size of the elfcorehdr segment, and
+ * check it against the new elfcorehdr buffer.
+ */
+ mem = image->segment[image->elfcorehdr_index].mem;
+ memsz = image->segment[image->elfcorehdr_index].memsz;
+ if (elfsz > memsz) {
+ pr_err("update elfcorehdr elfsz %lu > memsz %lu",
+ elfsz, memsz);
+ goto out;
+ }
+
+ /*
+ * Copy new elfcorehdr over the old elfcorehdr at destination.
+ */
+ old_elfcorehdr = kmap_local_page(pfn_to_page(mem >> PAGE_SHIFT));
+ if (!old_elfcorehdr) {
+ pr_err("updating elfcorehdr failed\n");
+ goto out;
+ }
+
+ /*
+ * Temporarily invalidate the crash image while the
+ * elfcorehdr is updated.
+ */
+ xchg(&kexec_crash_image, NULL);
+ memcpy_flushcache(old_elfcorehdr, elfbuf, elfsz);
+ xchg(&kexec_crash_image, image);
+ kunmap_local(old_elfcorehdr);
+ pr_debug("updated elfcorehdr\n");
+
+out:
+ vfree(elfbuf);
+}
+#endif
--
2.31.1
On 01/05/23 at 10:17am, Eric DeVolder wrote:
......
> @@ -394,10 +409,37 @@ int crash_load_segments(struct kimage *image)
> if (ret)
> return ret;
>
> - image->elf_headers = kbuf.buffer;
> - image->elf_headers_sz = kbuf.bufsz;
> + image->elf_headers = kbuf.buffer;
> + image->elf_headers_sz = kbuf.bufsz;
> + kbuf.memsz = kbuf.bufsz;
> +
> + if (IS_ENABLED(CONFIG_CRASH_HOTPLUG)) {
> + /*
> + * Ensure the elfcorehdr segment large enough for hotplug changes.
> + * Start with VMCOREINFO and kernel_map.
> + */
> + unsigned long pnum = 2;
> +
> + if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
> + pnum += CONFIG_NR_CPUS_DEFAULT;
> +
> + if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
> + pnum += CRASH_MAX_MEMORY_RANGES;
Logic of pnum calculating is a little confusing to me. If I only enable
one of CONFIG_HOTPLUG_CPU and CONFIG_MEMORY_HOTPLUG, is it OK? Say I
only enable CONFIG_HOTPLUG_CPU and CONFIG_SMP, on x86_64,
CONFIG_NR_CPUS_DEFAULT will be 64. pnum will be 64, is it OK. Am I miss
anything?
> +
> + if (pnum < (unsigned long)PN_XNUM) {
> + kbuf.memsz = pnum * sizeof(Elf64_Phdr);
> + kbuf.memsz += sizeof(Elf64_Ehdr);
> +
> + image->elfcorehdr_index = image->nr_segments;
> + image->elfcorehdr_index_valid = true;
> +
> + /* Mark as usable to crash kernel, else crash kernel fails on boot */
> + image->elf_headers_sz = kbuf.memsz;
> + } else {
> + pr_err("number of Phdrs %lu exceeds max\n", pnum);
> + }
> + }
>
> - kbuf.memsz = kbuf.bufsz;
> kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
> kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
> ret = kexec_add_buffer(&kbuf);
> @@ -412,3 +454,67 @@ int crash_load_segments(struct kimage *image)
> return ret;
> }
> #endif /* CONFIG_KEXEC_FILE */
On 1/9/23 01:36, Baoquan He wrote:
> On 01/05/23 at 10:17am, Eric DeVolder wrote:
> ......
>> @@ -394,10 +409,37 @@ int crash_load_segments(struct kimage *image)
>> if (ret)
>> return ret;
>>
>> - image->elf_headers = kbuf.buffer;
>> - image->elf_headers_sz = kbuf.bufsz;
>> + image->elf_headers = kbuf.buffer;
>> + image->elf_headers_sz = kbuf.bufsz;
>> + kbuf.memsz = kbuf.bufsz;
>> +
>> + if (IS_ENABLED(CONFIG_CRASH_HOTPLUG)) {
>> + /*
>> + * Ensure the elfcorehdr segment large enough for hotplug changes.
>> + * Start with VMCOREINFO and kernel_map.
>> + */
>> + unsigned long pnum = 2;
>> +
>> + if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
>> + pnum += CONFIG_NR_CPUS_DEFAULT;
>> +
>> + if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
>> + pnum += CRASH_MAX_MEMORY_RANGES;
>
> Logic of pnum calculating is a little confusing to me. If I only enable
> one of CONFIG_HOTPLUG_CPU and CONFIG_MEMORY_HOTPLUG, is it OK? Say I
> only enable CONFIG_HOTPLUG_CPU and CONFIG_SMP, on x86_64,
> CONFIG_NR_CPUS_DEFAULT will be 64. pnum will be 64, is it OK. Am I miss
> anything?
Ah, your understanding is correct, and the issue you point out I need to fix.
Specifically is only one of HOTPLUG_CPU or MEMORY_HOTPLUG is set, then I need
to allow a default for the other. Using the example you have above, there would
not be room for a single memory region, so I need to allow for a default number
of memory regions.
Good find!
eric
>
>> +
>> + if (pnum < (unsigned long)PN_XNUM) {
>> + kbuf.memsz = pnum * sizeof(Elf64_Phdr);
>> + kbuf.memsz += sizeof(Elf64_Ehdr);
>> +
>> + image->elfcorehdr_index = image->nr_segments;
>> + image->elfcorehdr_index_valid = true;
>> +
>> + /* Mark as usable to crash kernel, else crash kernel fails on boot */
>> + image->elf_headers_sz = kbuf.memsz;
>> + } else {
>> + pr_err("number of Phdrs %lu exceeds max\n", pnum);
>> + }
>> + }
>>
>> - kbuf.memsz = kbuf.bufsz;
>> kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
>> kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
>> ret = kexec_add_buffer(&kbuf);
>> @@ -412,3 +454,67 @@ int crash_load_segments(struct kimage *image)
>> return ret;
>> }
>> #endif /* CONFIG_KEXEC_FILE */
>
On 01/09/23 at 01:43pm, Eric DeVolder wrote:
>
>
> On 1/9/23 01:36, Baoquan He wrote:
> > On 01/05/23 at 10:17am, Eric DeVolder wrote:
> > ......
> > > @@ -394,10 +409,37 @@ int crash_load_segments(struct kimage *image)
> > > if (ret)
> > > return ret;
> > > - image->elf_headers = kbuf.buffer;
> > > - image->elf_headers_sz = kbuf.bufsz;
> > > + image->elf_headers = kbuf.buffer;
> > > + image->elf_headers_sz = kbuf.bufsz;
> > > + kbuf.memsz = kbuf.bufsz;
> > > +
> > > + if (IS_ENABLED(CONFIG_CRASH_HOTPLUG)) {
> > > + /*
> > > + * Ensure the elfcorehdr segment large enough for hotplug changes.
> > > + * Start with VMCOREINFO and kernel_map.
> > > + */
> > > + unsigned long pnum = 2;
> > > +
> > > + if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
> > > + pnum += CONFIG_NR_CPUS_DEFAULT;
> > > +
> > > + if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
> > > + pnum += CRASH_MAX_MEMORY_RANGES;
> >
> > Logic of pnum calculating is a little confusing to me. If I only enable
> > one of CONFIG_HOTPLUG_CPU and CONFIG_MEMORY_HOTPLUG, is it OK? Say I
> > only enable CONFIG_HOTPLUG_CPU and CONFIG_SMP, on x86_64,
> > CONFIG_NR_CPUS_DEFAULT will be 64. pnum will be 64, is it OK. Am I miss
> > anything?
>
> Ah, your understanding is correct, and the issue you point out I need to fix.
> Specifically is only one of HOTPLUG_CPU or MEMORY_HOTPLUG is set, then I need
> to allow a default for the other. Using the example you have above, there would
> not be room for a single memory region, so I need to allow for a default number
> of memory regions.
Hmm, for the above example, should we get real number of memory
regions? I am worried if the default number of memory regions
need be big enough. Because on system w/o memory hotplug, it could have
very many memory regions. The cpu number is similar.