linux-kernel - [PATCH 5/6] LoongArch/kexec_file: Add "mem" parameter to limit memory usage of kdump kernel

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Message-Id: <20250811092659.14903-6-youling.tang@linux.dev>
Date: Mon, 11 Aug 2025 17:26:58 +0800
From: Youling Tang <youling.tang@...ux.dev>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: WANG Xuerui <kernel@...0n.name>,
	Baoquan He <bhe@...hat.com>,
	kexec@...ts.infradead.org,
	loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	youling.tang@...ux.dev,
	Youling Tang <tangyouling@...inos.cn>
Subject: [PATCH 5/6] LoongArch/kexec_file: Add "mem" parameter to limit memory usage of kdump kernel

From: Youling Tang <tangyouling@...inos.cn>

Add the "mem=size@...rt" parameter to the cmdline and pass it to the
capture kernel. Limit the runtime memory area for capturing the kernel
to avoid disrupting the production kernel site.

Signed-off-by: Youling Tang <tangyouling@...inos.cn>
---
 arch/loongarch/kernel/machine_kexec_file.c | 24 ++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/arch/loongarch/kernel/machine_kexec_file.c b/arch/loongarch/kernel/machine_kexec_file.c
index 06def654cc09..7da88c80cace 100644
--- a/arch/loongarch/kernel/machine_kexec_file.c
+++ b/arch/loongarch/kernel/machine_kexec_file.c
@@ -89,6 +89,26 @@ static void cmdline_add_elfcorehdr(struct kimage *image, unsigned long *cmdline_
 	*cmdline_tmplen += elfcorehdr_strlen;
 }
 
+/*
+ * Adds the "mem=size@...rt" command line parameter to command line, indicating the
+ * memory region the new kernel can use to boot into.
+ */
+static void cmdline_add_mem(struct kimage *image, unsigned long *cmdline_tmplen,
+				char *modified_cmdline)
+{
+	int mem_strlen = 0;
+
+	mem_strlen = sprintf(modified_cmdline + (*cmdline_tmplen), "mem=0x%llx@...llx ",
+		crashk_res.end - crashk_res.start + 1, crashk_res.start);
+	*cmdline_tmplen += mem_strlen;
+
+	if (crashk_low_res.end) {
+		mem_strlen = sprintf(modified_cmdline + (*cmdline_tmplen), "mem=0x%llx@...llx ",
+			crashk_low_res.end - crashk_low_res.start + 1, crashk_low_res.start);
+		*cmdline_tmplen += mem_strlen;
+	}
+}
+
 #endif
 
 /* Adds the "initrd=start,size" command line parameter to command line. */
@@ -136,6 +156,7 @@ int load_other_segments(struct kimage *image,
 	/* load elf core header */
 	void *headers;
 	unsigned long headers_sz;
+
 	if (image->type == KEXEC_TYPE_CRASH) {
 		ret = prepare_elf_headers(&headers, &headers_sz);
 		if (ret) {
@@ -165,6 +186,9 @@ int load_other_segments(struct kimage *image,
 
 		/* Add the elfcorehdr=size@...rt parameter to the command line */
 		cmdline_add_elfcorehdr(image, &cmdline_tmplen, modified_cmdline, headers_sz);
+
+		/* Add the mem=size@...rt parameter to the command line */
+		cmdline_add_mem(image, &cmdline_tmplen, modified_cmdline);
 	}
 #endif
 
-- 
2.34.1