Re: [PATCH v4 09/10] crash hp: Add x86 crash hotplug support for kexec_file_load
From: Eric DeVolder
Date: Tue Mar 01 2022 - 15:12:42 EST
On 2/22/22 22:10, Baoquan He wrote:
On 02/09/22 at 02:57pm, Eric DeVolder wrote:
For x86_64, when CPU or memory is hot un/plugged, the crash
elfcorehdr, which describes the CPUs and memory in the system,
must also be updated.
Please mark the patch as X86 related by adding:
x86/kexec: Add x86 crash hotplug support for kexec_file_load
Done!
And also update other subject to reflect under which component the
changes are made, crash hp is the feature name.
Here's what I have at the moment, is this matching expectation?
pick 891fcff41a8f crash: fix minor typo/bug in debug message
pick 8f44e0d695be crash hp: Introduce CRASH_HOTPLUG configuration options
pick bae60e9db6ad crash: prototype change for crash_prepare_elf64_headers
pick cb98d1d923c8 crash: generic crash hotplug support infrastructure
pick 40e4434abad4 kexec: exclude elfcorehdr from the segment digest
pick 75039922aedc kexec: exclude hot remove cpu from elfcorehdr notes
pick 0be483dadeb8 x86/kexec: Add x86 crash hotplug support for kexec_file_load
pick 388bb5e4bf9a x86/kexec: Add x86 crash hotplug support for kexec_load
Otherwise, this looks good to me.
Thanks!
eric
To update the elfcorehdr for x86_64, a new elfcorehdr must be
generated from the available CPUs and memory. The new elfcorehdr
is prepared into a buffer, and if no errors occur, it is
installed over the top of the existing elfcorehdr.
In the patch 'crash hp: 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_HOTPLUG_ELFCOREHDR_SZ configure item.
With this change, the kexec_file_load syscall (not kexec_load)
is supported. When loading the crash kernel via kexec_file_load,
the elfcorehdr is identified at load time in crash_load_segments().
Signed-off-by: Eric DeVolder <eric.devolder@xxxxxxxxxx>
---
arch/x86/kernel/crash.c | 92 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 92 insertions(+)
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 9db41cce8d97..6215c51919db 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -25,6 +25,7 @@
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/memblock.h>
+#include <linux/highmem.h>
#include <asm/processor.h>
#include <asm/hardirq.h>
@@ -398,7 +399,17 @@ int crash_load_segments(struct kimage *image)
image->elf_headers = kbuf.buffer;
image->elf_headers_sz = kbuf.bufsz;
+#ifdef CONFIG_CRASH_HOTPLUG
+ /* Ensure elfcorehdr segment large enough for hotplug changes */
+ kbuf.memsz = CONFIG_CRASH_HOTPLUG_ELFCOREHDR_SZ;
+ /* For marking as usable to crash kernel */
+ image->elf_headers_sz = kbuf.memsz;
+ /* Record the index of the elfcorehdr segment */
+ image->elf_index = image->nr_segments;
+ image->elf_index_valid = true;
+#else
kbuf.memsz = kbuf.bufsz;
+#endif
kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
ret = kexec_add_buffer(&kbuf);
@@ -413,3 +424,84 @@ int crash_load_segments(struct kimage *image)
return ret;
}
#endif /* CONFIG_KEXEC_FILE */
+
+#ifdef CONFIG_CRASH_HOTPLUG
+/**
+ * arch_crash_hotplug_handler() - Handle hotplug elfcorehdr changes
+ * @image: the active struct kimage
+ * @hp_action: the hot un/plug action being handled
+ * @a: first parameter dependent upon hp_action
+ * @b: first parameter dependent upon hp_action
+ *
+ * To accurately reflect hot un/plug changes, the elfcorehdr (which
+ * is passed to the crash kernel via the elfcorehdr= parameter)
+ * must be updated with the new list of CPUs and memories. The new
+ * elfcorehdr is prepared in a kernel buffer, and if no errors,
+ * then it is written on top of the existing/old elfcorehdr.
+ *
+ * For hotplug changes to elfcorehdr to work, two conditions are
+ * needed:
+ * First, the segment containing the elfcorehdr must be large enough
+ * to permit a growing number of resources. See
+ * CONFIG_CRASH_HOTPLUG_ELFCOREHDR_SZ.
+ * Second, purgatory must explicitly exclude the elfcorehdr from the
+ * list of segments it checks (since the elfcorehdr changes and thus
+ * would require an update to purgatory itself to update the digest).
+ *
+ */
+void arch_crash_hotplug_handler(struct kimage *image,
+ unsigned int hp_action, unsigned long a, unsigned long b)
+{
+ struct kexec_segment *ksegment;
+ unsigned char *ptr = NULL;
+ unsigned long elfsz = 0;
+ void *elfbuf = NULL;
+ unsigned long mem, memsz;
+
+ /* Must have valid elfcorehdr index */
+ if (!image->elf_index_valid) {
+ pr_err("crash hp: unable to locate elfcorehdr segment");
+ goto out;
+ }
+
+ ksegment = &image->segment[image->elf_index];
+ mem = ksegment->mem;
+ memsz = ksegment->memsz;
+
+ /*
+ * Create the new elfcorehdr reflecting the changes to CPU and/or
+ * memory resources. The elfcorehdr segment memsz must be
+ * sufficiently large to accommodate increases due to hotplug
+ * activity. See CRASH_HOTPLUG_ELFCOREHDR_SZ.
+ */
+ if (prepare_elf_headers(image, &elfbuf, &elfsz)) {
+ pr_err("crash hp: unable to prepare elfcore headers");
+ goto out;
+ }
+ if (elfsz > memsz) {
+ pr_err("crash hp: update elfcorehdr elfsz %lu > memsz %lu",
+ elfsz, memsz);
+ goto out;
+ }
+
+ /*
+ * At this point, we are all but assured of success.
+ * Copy new elfcorehdr into destination.
+ */
+ ptr = map_crash_pages(mem, memsz);
+ if (ptr) {
+ /* Temporarily invalidate the crash image while it is replaced */
+ xchg(&kexec_crash_image, NULL);
+ /* Write the new elfcorehdr into memory */
+ memcpy_flushcache((void *)ptr, elfbuf, elfsz);
+ /* The crash image is now valid once again */
+ xchg(&kexec_crash_image, image);
+ }
+ unmap_crash_pages((void **)&ptr);
+ pr_debug("crash hp: re-loaded elfcorehdr at 0x%lx\n", mem);
+
+out:
+ if (elfbuf)
+ vfree(elfbuf);
+}
+#endif /* CONFIG_CRASH_HOTPLUG */
--
2.27.0