[PATCH v27 5/8] x86/crash: add x86 crash hotplug support

Eric DeVolder
2023-08-11T17:07:36Z

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.

A new elfcorehdr is generated from the available CPUs and memory
and replaces the existing elfcorehdr. The segment containing the
elfcorehdr is identified at run-time in
crash_core:crash_handle_hotplug_event().

No modifications to purgatory (see 'kexec: exclude elfcorehdr
from the segment digest') or boot_params (as the elfcorehdr=
capture kernel command line parameter pointer remains unchanged
and correct) are needed, just elfcorehdr.

For kexec_file_load(), the elfcorehdr segment size is based on
NR_CPUS and CRASH_MAX_MEMORY_RANGES in order to accommodate a
growing number of CPU and memory resources.

For kexec_load(), the userspace kexec utility needs to size the
elfcorehdr segment in the same/similar manner.

To accommodate kexec_load() syscall in the absence of
kexec_file_load() syscall support, prepare_elf_headers() and
dependents are moved outside of CONFIG_KEXEC_FILE.

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
Reviewed-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Acked-by: Hari Bathini <hbathini@linux.ibm.com>
Acked-by: Baoquan He <bhe@redhat.com>
---
arch/x86/Kconfig | 3 +
arch/x86/include/asm/kexec.h | 15 +++++
arch/x86/kernel/crash.c | 103 ++++++++++++++++++++++++++++++++---
3 files changed, 114 insertions(+), 7 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 7082fc10b346..ffc95c3d6abd 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2069,6 +2069,9 @@ config ARCH_SUPPORTS_KEXEC_JUMP
config ARCH_SUPPORTS_CRASH_DUMP
def_bool X86_64 || (X86_32 && HIGHMEM)

+config ARCH_SUPPORTS_CRASH_HOTPLUG
+ def_bool y
+
config PHYSICAL_START
hex "Physical address where the kernel is loaded" if (EXPERT || CRASH_DUMP)
default "0x1000000"
diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
index 5b77bbc28f96..9143100ea3ea 100644
--- a/arch/x86/include/asm/kexec.h
+++ b/arch/x86/include/asm/kexec.h
@@ -209,6 +209,21 @@ 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 cdd92ab43cda..c70a111c44fa 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -158,8 +158,6 @@ 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;
@@ -231,7 +229,7 @@ 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;
@@ -249,6 +247,9 @@ 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);

@@ -257,6 +258,7 @@ 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;
@@ -371,18 +373,42 @@ 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
+ /*
+ * The elfcorehdr segment size accounts for VMCOREINFO, kernel_map,
+ * maximum CPUs and maximum memory ranges.
+ */
+ if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
+ pnum = 2 + CONFIG_NR_CPUS_DEFAULT + CONFIG_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);
@@ -395,3 +421,66 @@ 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: a pointer to kexec_crash_image
+ *
+ * Prepare the new elfcorehdr and replace the existing 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 create new elfcorehdr");
+ 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("mapping elfcorehdr segment 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