Re: [PATCH v14 7/7] x86/crash: add x86 crash hotplug support
On 12/7/22 04:19, Borislav Petkov wrote:
On Wed, Nov 16, 2022 at 04:46:43PM -0500, Eric DeVolder wrote:
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
---
arch/x86/Kconfig | 9 +++
arch/x86/include/asm/kexec.h | 15 +
arch/x86/kernel/crash.c | 106 ++-
3 files changed, 127 insertions(+), 3 deletions(-)
Some quick cleanups ontop, there's potential for more:
---
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ffee99046942..486509030d3a 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2091,13 +2091,16 @@ config CRASH_DUMP
For more details see Documentation/admin-guide/kdump/kdump.rst
config CRASH_HOTPLUG
- bool "kernel updates of crash elfcorehdr"
+ bool "Update the crash elfcorehdr on system configuration changes"
default n
depends on CRASH_DUMP && (HOTPLUG_CPU || MEMORY_HOTPLUG)
help
- Enable the kernel to directly update 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.
+ Enable direct updates 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.
Done!
config KEXEC_JUMP
bool "kexec jump"
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index d2238bcf8106..d26f208e582e 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -413,25 +413,32 @@ int crash_load_segments(struct kimage *image)
image->elf_headers_sz= kbuf.bufsz;
kbuf.memsz = kbuf.bufsz;
-#ifdef CONFIG_CRASH_HOTPLUG
- /* Ensure elfcorehdr segment large enough for hotplug changes */
- unsigned long pnum = 2; /* VMCOREINFO and kernel_map */
-
- 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);
+ 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);
+ }
Done, converted this block to an IS_ENABLED(CONFIG_CRASH_HOTPLUG).
}
-#endif
kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
@@ -463,10 +470,9 @@ int crash_load_segments(struct kimage *image)
*/
void
Re: [PATCH v14 7/7] x86/crash: add x86 crash hotplug support
On Wed, Nov 16, 2022 at 04:46:43PM -0500, Eric DeVolder wrote:
> 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
> ---
> arch/x86/Kconfig | 9 +++
> arch/x86/include/asm/kexec.h | 15 +
> arch/x86/kernel/crash.c | 106 ++-
> 3 files changed, 127 insertions(+), 3 deletions(-)
Some quick cleanups ontop, there's potential for more:
---
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ffee99046942..486509030d3a 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2091,13 +2091,16 @@ config CRASH_DUMP
For more details see Documentation/admin-guide/kdump/kdump.rst
config CRASH_HOTPLUG
- bool "kernel updates of crash elfcorehdr"
+ bool "Update the crash elfcorehdr on system configuration changes"
default n
depends on CRASH_DUMP && (HOTPLUG_CPU || MEMORY_HOTPLUG)
help
- Enable the kernel to directly update 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.
+ Enable direct updates 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"
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index d2238bcf8106..d26f208e582e 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -413,25 +413,32 @@ int crash_load_segments(struct kimage *image)
image->elf_headers_sz = kbuf.bufsz;
kbuf.memsz = kbuf.bufsz;
-#ifdef CONFIG_CRASH_HOTPLUG
- /* Ensure elfcorehdr segment large enough for hotplug changes */
- unsigned long pnum = 2; /* VMCOREINFO and kernel_map */
-
- 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);
+ 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);
+ }
}
-#endif
kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
@@ -463,10 +470,9 @@ int crash_load_segments(struct kimage *image)
*/
void arch_crash_handle_hotplug_event(struct kimage *image)
{
+ void *elfbuf, *old_elfcorehdr;
unsigned long
[PATCH v14 7/7] x86/crash: add x86 crash hotplug support
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
---
arch/x86/Kconfig | 9 +++
arch/x86/include/asm/kexec.h | 15 +
arch/x86/kernel/crash.c | 106 ++-
3 files changed, 127 insertions(+), 3 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 67745ceab0db..fc7b6457a0b4 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2072,6 +2072,15 @@ config CRASH_DUMP
(CONFIG_RELOCATABLE=y).
For more details see Documentation/admin-guide/kdump/kdump.rst
+config CRASH_HOTPLUG
+ bool "kernel updates of crash elfcorehdr"
+ default n
+ depends on CRASH_DUMP && (HOTPLUG_CPU || MEMORY_HOTPLUG)
+ help
+ Enable the kernel to directly update 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.
+
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..d2238bcf8106 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -42,6 +42,21 @@
#include
#include
+/*
+ * 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 +409,30 @@ 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;
+
+#ifdef CONFIG_CRASH_HOTPLUG
+ /* Ensure elfcorehdr segment large enough for hotplug changes */
+ unsigned long pnum = 2; /* VMCOREINFO and kernel_map */
+
+ 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 */
+
