linux-kernel - [PATCH v8 7/7] x86/crash: Add x86 crash hotplug support for kexec

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Date:   Thu,  5 May 2022 14:46:03 -0400
From:   Eric DeVolder <eric.devolder@...cle.com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org,
        kexec@...ts.infradead.org, ebiederm@...ssion.com,
        dyoung@...hat.com, bhe@...hat.com, vgoyal@...hat.com
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com,
        nramas@...ux.microsoft.com, thomas.lendacky@....com,
        robh@...nel.org, efault@....de, rppt@...nel.org, david@...hat.com,
        konrad.wilk@...cle.com, boris.ostrovsky@...cle.com,
        eric.devolder@...cle.com
Subject: [PATCH v8 7/7] x86/crash: Add x86 crash hotplug support for kexec_load

For kexec_file_load support, the loading of the crash kernel occurs
entirely within the kernel, and as such the elfcorehdr is readily
identified (so that it can be modified upon hotplug events).

This change enables support for kexec_load by identifying the
elfcorehdr segment in the arch_crash_handle_hotplug_event(),
if it has not already been identified.

Signed-off-by: Eric DeVolder <eric.devolder@...cle.com>
Acked-by: Baoquan He <bhe@...hat.com>
---
 arch/x86/kernel/crash.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 951ef365f0a7..845d7c77854d 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -485,6 +485,30 @@ void arch_crash_handle_hotplug_event(struct kimage *image,
 	void *elfbuf = NULL;
 	unsigned long mem, memsz;
 
+	/*
+	 * When the struct kimage is alloced, it is wiped to zero, so
+	 * the elfcorehdr_index_valid defaults to false. It is set on the
+	 * kexec_file_load path, or here for kexec_load, if not already
+	 * identified.
+	 */
+	if (!image->elfcorehdr_index_valid) {
+		unsigned int n;
+
+		for (n = 0; n < image->nr_segments; n++) {
+			mem = image->segment[n].mem;
+			memsz = image->segment[n].memsz;
+			ptr = map_crash_pages(mem, memsz);
+			if (ptr) {
+				/* The segment containing elfcorehdr */
+				if (memcmp(ptr, ELFMAG, SELFMAG) == 0) {
+					image->elfcorehdr_index = (int)n;
+					image->elfcorehdr_index_valid = true;
+				}
+			}
+			unmap_crash_pages((void **)&ptr);
+		}
+	}
+
 	if (!image->elfcorehdr_index_valid) {
 		pr_err("crash hp: unable to locate elfcorehdr segment");
 		goto out;
-- 
2.27.0