[v14,7/7] x86/crash: add x86 crash hotplug support
Commit Message
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 <eric.devolder@oracle.com>
---
arch/x86/Kconfig | 9 +++
arch/x86/include/asm/kexec.h | 15 +++++
arch/x86/kernel/crash.c | 106 ++++++++++++++++++++++++++++++++++-
3 files changed, 127 insertions(+), 3 deletions(-)
Comments
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 <eric.devolder@oracle.com>
> ---
> 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 mem, memsz;
- unsigned long elfsz = 0;
- void *elfbuf = NULL;
- void *ptr;
+ unsigned long elfsz;
/*
* Create the new elfcorehdr reflecting the changes to CPU and/or
@@ -489,26 +495,24 @@ void arch_crash_handle_hotplug_event(struct kimage *image)
goto out;
}
- /*
- * Copy new elfcorehdr over the old elfcorehdr at destination.
- */
- ptr = arch_map_crash_pages(mem, memsz);
- if (ptr) {
- /*
- * Temporarily invalidate the crash image while the
- * elfcorehdr is updated.
- */
- xchg(&kexec_crash_image, NULL);
- memcpy_flushcache(ptr, elfbuf, elfsz);
- xchg(&kexec_crash_image, image);
- arch_unmap_crash_pages(ptr);
- pr_debug("updated elfcorehdr\n");
- } else {
+ /* Copy new elfcorehdr over the old elfcorehdr at destination. */
+ old_elfcorehdr = arch_map_crash_pages(mem, memsz);
+ 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);
+ arch_unmap_crash_pages(old_elfcorehdr);
+ pr_debug("updated elfcorehdr\n");
+
out:
- if (elfbuf)
- vfree(elfbuf);
+ vfree(elfbuf);
}
#endif
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 <eric.devolder@oracle.com>
>> ---
>> 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 arch_crash_handle_hotplug_event(struct kimage *image)
> {
> + void *elfbuf, *old_elfcorehdr;
> unsigned long mem, memsz;
> - unsigned long elfsz = 0;
> - void *elfbuf = NULL;
> - void *ptr;
> + unsigned long elfsz;
Done, note that I leave elfbuf initialized to NULL as its use in prepare_elf_headers() does not
necessarily write it, so it could otherwise have been used uninitialized.
>
> /*
> * Create the new elfcorehdr reflecting the changes to CPU and/or
> @@ -489,26 +495,24 @@ void arch_crash_handle_hotplug_event(struct kimage *image)
> goto out;
> }
>
> - /*
> - * Copy new elfcorehdr over the old elfcorehdr at destination.
> - */
> - ptr = arch_map_crash_pages(mem, memsz);
> - if (ptr) {
> - /*
> - * Temporarily invalidate the crash image while the
> - * elfcorehdr is updated.
> - */
> - xchg(&kexec_crash_image, NULL);
> - memcpy_flushcache(ptr, elfbuf, elfsz);
> - xchg(&kexec_crash_image, image);
> - arch_unmap_crash_pages(ptr);
> - pr_debug("updated elfcorehdr\n");
> - } else {
> + /* Copy new elfcorehdr over the old elfcorehdr at destination. */
> + old_elfcorehdr = arch_map_crash_pages(mem, memsz);
> + if (!old_elfcorehdr) {
> pr_err("updating elfcorehdr failed\n");
> + goto out;
> }
Done, changed to old_elfcorehdr and error/early-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);
> + arch_unmap_crash_pages(old_elfcorehdr);
> + pr_debug("updated elfcorehdr\n");
> +
> out:
> - if (elfbuf)
> - vfree(elfbuf);
> + vfree(elfbuf);
> }
> #endif
>
Done.
Thanks!
eric
@@ -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
@@ -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 */
@@ -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 +409,30 @@ 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 */
+ image->elf_headers_sz = kbuf.memsz;
+ } else {
+ pr_err("number of Phdrs %lu exceeds max\n", pnum);
+ }
+#endif
- kbuf.memsz = kbuf.bufsz;
kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
ret = kexec_add_buffer(&kbuf);
@@ -412,3 +447,68 @@ 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)
+{
+ unsigned long mem, memsz;
+ unsigned long elfsz = 0;
+ void *elfbuf = NULL;
+ void *ptr;
+
+ /*
+ * 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.
+ */
+ ptr = arch_map_crash_pages(mem, memsz);
+ if (ptr) {
+ /*
+ * Temporarily invalidate the crash image while the
+ * elfcorehdr is updated.
+ */
+ xchg(&kexec_crash_image, NULL);
+ memcpy_flushcache(ptr, elfbuf, elfsz);
+ xchg(&kexec_crash_image, image);
+ arch_unmap_crash_pages(ptr);
+ pr_debug("updated elfcorehdr\n");
+ } else {
+ pr_err("updating elfcorehdr failed\n");
+ }
+
+out:
+ if (elfbuf)
+ vfree(elfbuf);
+}
+#endif