[PATCH] LoongArch: kdump: add arch_crash_save_vmcoreinfo() support

[Yangyang Lian]

Since commit 23c85094fe18 ("proc/kcore: add vmcoreinfo note to
/proc/kcore") the kernel has exported the vmcoreinfo PT_NOTE on
/proc/kcore as wellas /proc/vmcore.

LoongArch does not provide arch_crash_save_vmcoreinfo(), so the
arch-specific values are missing from the vmcoreinfo PT_NOTE. The
generic exporter in kernel/vmcore_info.c already provides
NUMBER(VMALLOC_START), but tools like crash cannot derive the module
and vmemmap ranges, VA_BITS, or the KASLR offset of a LoongArch dump.

Since commit 18210a104bb9 ("LoongArch: Expand module virtual address
space to 2GB") the vmalloc and module boundaries are no longer stable
across kernel versions either, so vmcoreinfo is the only reliable
source for them.

Provide this function in a separate file that is built at the same time
as its caller in kernel/vmcore_info.c, and add a LOONGARCH64 section to
Documentation/admin-guide/kdump/vmcoreinfo.rst.

Reported-by: Haoran Jiang <jianghaoran@xxxxxxxxxx>
Suggested-by: Haoran Jiang <jianghaoran@xxxxxxxxxx>
Co-developed-by: George Guo <guodongtai@xxxxxxxxxx>
Signed-off-by: George Guo <guodongtai@xxxxxxxxxx>
Signed-off-by: Yangyang Lian <lianyangyang@xxxxxxxxxx>
---
 .../admin-guide/kdump/vmcoreinfo.rst          | 29 +++++++++++++++++++
 arch/loongarch/kernel/Makefile                |  1 +
 arch/loongarch/kernel/vmcore_info.c           | 21 ++++++++++++++
 3 files changed, 51 insertions(+)
 create mode 100644 arch/loongarch/kernel/vmcore_info.c

diff --git a/Documentation/admin-guide/kdump/vmcoreinfo.rst b/Documentation/admin-guide/kdump/vmcoreinfo.rst
index 7663c610fe90..2ff921232616 100644
--- a/Documentation/admin-guide/kdump/vmcoreinfo.rst
+++ b/Documentation/admin-guide/kdump/vmcoreinfo.rst
@@ -594,3 +594,32 @@ va_kernel_pa_offset
 
 Indicates the offset between the kernel virtual and physical mappings.
 Used to translate virtual to physical addresses.
+
+LOONGARCH64
+===========
+
+VA_BITS
+-------
+
+The maximum number of bits for virtual addresses. Used to compute the
+virtual memory ranges.
+
+PHYS_OFFSET
+-----------
+
+Indicates the physical address of the start of memory. Used to translate
+virtual to physical addresses.
+
+KERNELOFFSET
+------------
+
+The kernel randomization offset. Used to locate the kernel text in
+virtual memory. If KASLR is disabled, this value is zero.
+
+MODULES_VADDR|MODULES_END|VMALLOC_START|VMALLOC_END|VMEMMAP_START|VMEMMAP_END
+-----------------------------------------------------------------------------
+
+Used to get the correct ranges:
+	MODULES_VADDR ~ MODULES_END-1 : Kernel module space.
+	VMALLOC_START ~ VMALLOC_END-1 : vmalloc() / ioremap() space.
+	VMEMMAP_START ~ VMEMMAP_END-1 : vmemmap region, used for struct page array.
diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
index 001924877772..6260c15adaba 100644
--- a/arch/loongarch/kernel/Makefile
+++ b/arch/loongarch/kernel/Makefile
@@ -64,6 +64,7 @@ obj-$(CONFIG_RELOCATABLE)	+= relocate.o
 obj-$(CONFIG_KEXEC_CORE)	+= machine_kexec.o relocate_kernel.o
 obj-$(CONFIG_KEXEC_FILE)	+= machine_kexec_file.o kexec_efi.o kexec_elf.o
 obj-$(CONFIG_CRASH_DUMP)	+= crash_dump.o
+obj-$(CONFIG_VMCORE_INFO)	+= vmcore_info.o
 
 obj-$(CONFIG_UNWINDER_GUESS)	+= unwind_guess.o
 obj-$(CONFIG_UNWINDER_PROLOGUE) += unwind_prologue.o
diff --git a/arch/loongarch/kernel/vmcore_info.c b/arch/loongarch/kernel/vmcore_info.c
new file mode 100644
index 000000000000..1128f6cdfe0d
--- /dev/null
+++ b/arch/loongarch/kernel/vmcore_info.c
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/vmcore_info.h>
+#include <asm/addrspace.h>
+#include <asm/pgtable.h>
+#include <asm/setup.h>
+
+void arch_crash_save_vmcoreinfo(void)
+{
+	VMCOREINFO_NUMBER(VA_BITS);
+	/* NUMBER(VMALLOC_START) is exported by the generic code */
+	vmcoreinfo_append_str("NUMBER(VMALLOC_END)=0x%lx\n", VMALLOC_END);
+#ifdef CONFIG_64BIT
+	vmcoreinfo_append_str("NUMBER(MODULES_VADDR)=0x%lx\n", MODULES_VADDR);
+	vmcoreinfo_append_str("NUMBER(MODULES_END)=0x%lx\n", MODULES_END);
+	vmcoreinfo_append_str("NUMBER(VMEMMAP_START)=0x%lx\n", (unsigned long)vmemmap);
+	vmcoreinfo_append_str("NUMBER(VMEMMAP_END)=0x%lx\n", VMEMMAP_END);
+#endif
+	vmcoreinfo_append_str("NUMBER(PHYS_OFFSET)=0x%lx\n", PHYS_OFFSET);
+	vmcoreinfo_append_str("KERNELOFFSET=%lx\n", kaslr_offset());
+}
-- 
2.25.1