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Message-Id: <20230814214446.6659-9-eric.devolder@oracle.com>
Date: Mon, 14 Aug 2023 17:44:46 -0400
From: Eric DeVolder <eric.devolder@...cle.com>
To: linux-kernel@...r.kernel.org, david@...hat.com, osalvador@...e.de,
corbet@....net, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
dave.hansen@...ux.intel.com, x86@...nel.org, bhe@...hat.com,
ebiederm@...ssion.com, kexec@...ts.infradead.org
Cc: hpa@...or.com, gregkh@...uxfoundation.org, rafael@...nel.org,
vgoyal@...hat.com, dyoung@...hat.com, lf32.dev@...il.com,
akpm@...ux-foundation.org, naveen.n.rao@...ux.vnet.ibm.com,
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tiwai@...e.de, seanjc@...gle.com, linux@...ssschuh.net,
vschneid@...hat.com, linux-mm@...ck.org, linux-doc@...r.kernel.org,
sourabhjain@...ux.ibm.com, konrad.wilk@...cle.com,
boris.ostrovsky@...cle.com, eric.devolder@...cle.com
Subject: [PATCH v28 8/8] x86/crash: optimize CPU changes
crash_prepare_elf64_headers() writes into the elfcorehdr an ELF
PT_NOTE for all possible CPUs. As such, subsequent changes to CPUs
(ie. hot un/plug, online/offline) do not need to rewrite the elfcorehdr.
The kimage->file_mode term covers kdump images loaded via the
kexec_file_load() syscall. Since crash_prepare_elf64_headers()
wrote the initial elfcorehdr, no update to the elfcorehdr is
needed for CPU changes.
The kimage->elfcorehdr_updated term covers kdump images loaded via
the kexec_load() syscall. At least one memory or CPU change must occur
to cause crash_prepare_elf64_headers() to rewrite the elfcorehdr.
Afterwards, no update to the elfcorehdr is needed for CPU changes.
This code is intentionally *NOT* hoisted into
crash_handle_hotplug_event() as it would prevent the arch-specific
handler from running for CPU changes. This would break PPC, for
example, which needs to update other information besides the
elfcorehdr, on CPU changes.
Signed-off-by: Eric DeVolder <eric.devolder@...cle.com>
Reviewed-by: Sourabh Jain <sourabhjain@...ux.ibm.com>
Acked-by: Hari Bathini <hbathini@...ux.ibm.com>
Acked-by: Baoquan He <bhe@...hat.com>
---
arch/x86/kernel/crash.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 1900efcdf1bc..86d2ca80b9b2 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -469,6 +469,16 @@ void arch_crash_handle_hotplug_event(struct kimage *image)
unsigned long mem, memsz;
unsigned long elfsz = 0;
+ /*
+ * As crash_prepare_elf64_headers() has already described all
+ * possible CPUs, there is no need to update the elfcorehdr
+ * for additional CPU changes.
+ */
+ if ((image->file_mode || image->elfcorehdr_updated) &&
+ ((image->hp_action == KEXEC_CRASH_HP_ADD_CPU) ||
+ (image->hp_action == KEXEC_CRASH_HP_REMOVE_CPU)))
+ return;
+
/*
* Create the new elfcorehdr reflecting the changes to CPU and/or
* memory resources.
--
2.31.1
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