[PATCH v19 5/7] x86/crash: add x86 crash hotplug support
Eric DeVolder
eric.devolder at oracle.com
Mon Mar 6 08:22:26 PST 2023
When CPU or memory is hot un/plugged, or off/onlined, the crash
elfcorehdr, which describes the CPUs and memory in the system,
must also be updated.
The segment containing the elfcorehdr is identified at run-time
in crash_core:crash_handle_hotplug_event(), which works for both
the kexec_load() and kexec_file_load() syscalls. A new elfcorehdr
is generated from the available CPUs and memory 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 description. This is used
only on the kexec_file_load() syscall; for kexec_load() userspace
will need to size the segment similarly.
To accommodate kexec_load() syscall in the absence of
kexec_file_load() syscall support, and with CONFIG_CRASH_HOTPLUG
enabled, it is necessary to move prepare_elf_headers() and
dependents outside of CONFIG_KEXEC_FILE.
Signed-off-by: Eric DeVolder <eric.devolder at oracle.com>
---
arch/x86/Kconfig | 13 ++++
arch/x86/include/asm/kexec.h | 15 +++++
arch/x86/kernel/crash.c | 119 ++++++++++++++++++++++++++++++++---
3 files changed, 140 insertions(+), 7 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 3604074a878b..2ca5e19b8f19 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2119,6 +2119,19 @@ 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 or online/offline 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 305514431f26..c9aaec9de775 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;
@@ -173,8 +188,6 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
crash_save_cpu(regs, safe_smp_processor_id());
}
-#ifdef CONFIG_KEXEC_FILE
-
static int get_nr_ram_ranges_callback(struct resource *res, void *arg)
{
unsigned int *nr_ranges = arg;
@@ -246,7 +259,7 @@ static int prepare_elf64_ram_headers_callback(struct resource *res, void *arg)
/* Prepare elf headers. Return addr and size */
static int prepare_elf_headers(struct kimage *image, void **addr,
- unsigned long *sz)
+ unsigned long *sz, unsigned long *nr_mem_ranges)
{
struct crash_mem *cmem;
int ret;
@@ -264,6 +277,9 @@ static int prepare_elf_headers(struct kimage *image, void **addr,
if (ret)
goto out;
+ /* Return the computed number of memory ranges, for hotplug usage */
+ *nr_mem_ranges = cmem->nr_ranges;
+
/* By default prepare 64bit headers */
ret = crash_prepare_elf64_headers(cmem, IS_ENABLED(CONFIG_X86_64), addr, sz);
@@ -272,6 +288,7 @@ static int prepare_elf_headers(struct kimage *image, void **addr,
return ret;
}
+#ifdef CONFIG_KEXEC_FILE
static int add_e820_entry(struct boot_params *params, struct e820_entry *entry)
{
unsigned int nr_e820_entries;
@@ -386,18 +403,42 @@ int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
int crash_load_segments(struct kimage *image)
{
int ret;
+ unsigned long pnum = 0;
struct kexec_buf kbuf = { .image = image, .buf_min = 0,
.buf_max = ULONG_MAX, .top_down = false };
/* Prepare elf headers and add a segment */
- ret = prepare_elf_headers(image, &kbuf.buffer, &kbuf.bufsz);
+ ret = prepare_elf_headers(image, &kbuf.buffer, &kbuf.bufsz, &pnum);
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 the elfcorehdr segment large enough for hotplug changes.
+ * Account for VMCOREINFO and kernel_map and maximum CPUs.
+ */
+ if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
+ pnum = 2 + CONFIG_NR_CPUS_DEFAULT + CRASH_MAX_MEMORY_RANGES;
+ else
+ pnum += 2 + CONFIG_NR_CPUS_DEFAULT;
+
+ if (pnum < (unsigned long)PN_XNUM) {
+ kbuf.memsz = pnum * sizeof(Elf64_Phdr);
+ kbuf.memsz += sizeof(Elf64_Ehdr);
+
+ image->elfcorehdr_index = image->nr_segments;
+
+ /* 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);
@@ -410,3 +451,67 @@ 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
+ *
+ * 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 nr_mem_ranges;
+ 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, &nr_mem_ranges)) {
+ 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
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